Work around a Go bug when parsing timezones

[lupine]

On my machine, which has a local time of +0100, commits with a timezone of +0000 adopt the local timezone. This is noted as a bug in golang/go#19750 - assigned to the Go 1.9 milestone.

This workaround fixes commit timezone parsing in the interim.

I don't know a way to reproduce this error in a test case, so there are no spec changes, but I've manually tested the change and it does resolve the issue for me locally. Here's the same test case, before and after:

=== RUN   TestIndexingGitlabTest
2017/03/30 19:32:18 Indexing from 0000000000000000000000000000000000000000 to b83d6e391c22777fca1ed3012fce84f633d7fed0
2017/03/30 19:32:18 Index: gitlab-test-1490898738, Project ID: 667
--- FAIL: TestIndexingGitlabTest (0.75s)
        Error Trace:    integration_test.go:163
        Error:          Not equal:
                        expected: map[string]interface {}{"type":"commit", "sha":"b83d6e391c22777fca1ed3012fce84f633d7fed0", "author":map[string]interface {}{"email":"[email protected]", "name":"Job van der Voort", "time":"20160927T143746+0000"}, "committer":map[string]interface {}{"name":"Job van der Voort", "time":"20160927T143746+0000", "email":"[email protected]"}, "rid":"667", "message":"Merge branch 'branch-merged' into 'master'\r\n\r\nadds bar folder and branch-test text file to check Repository merged_to_root_ref method\r\n\r\n\r\n\r\nSee merge request !12"}
                        received: map[string]interface {}{"rid":"667", "message":"Merge branch 'branch-merged' into 'master'\r\n\r\nadds bar folder and branch-test text file to check Repository merged_to_root_ref method\r\n\r\n\r\n\r\nSee merge request !12", "sha":"b83d6e391c22777fca1ed3012fce84f633d7fed0", "type":"commit", "author":map[string]interface {}{"name":"Job van der Voort", "email":"[email protected]", "time":"20160927T153746+0100"}, "committer":map[string]interface {}{"name":"Job van der Voort", "email":"[email protected]", "time":"20160927T153746+0100"}}

                        Diff:
                        --- Expected
                        +++ Actual
                        @@ -4,3 +4,3 @@
                           (string) (len=4) "name": (string) (len=17) "Job van der Voort",
                        -  (string) (len=4) "time": (string) (len=20) "20160927T143746+0000"
                        +  (string) (len=4) "time": (string) (len=20) "20160927T153746+0100"
                          },
                        @@ -9,3 +9,3 @@
                           (string) (len=4) "name": (string) (len=17) "Job van der Voort",
                        -  (string) (len=4) "time": (string) (len=20) "20160927T143746+0000"
                        +  (string) (len=4) "time": (string) (len=20) "20160927T153746+0100"
                          },
FAIL

=== RUN   TestIndexingGitlabTest
2017/03/30 19:37:34 Indexing from 0000000000000000000000000000000000000000 to b83d6e391c22777fca1ed3012fce84f633d7fed0
2017/03/30 19:37:34 Index: gitlab-test-1490899054, Project ID: 667
--- PASS: TestIndexingGitlabTest (0.78s)
PASS

Closes #318

[lupine]

@mcuadros how's this?

[codecov]

Codecov Report

Merging #320 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #320   +/-   ##
=======================================
  Coverage   77.35%   77.35%           
=======================================
  Files         117      117           
  Lines        8015     8015           
=======================================
  Hits         6200     6200           
  Misses       1156     1156           
  Partials      659      659

Impacted Files	Coverage Δ
plumbing/object/object.go	67.39% <100%> (ø)	⬆️

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[mcuadros]

Please provide a test, since is a very arcane issue

[lupine]

@mcuadros my only reproducer involves changing the system time at the moment. I can keep hunting, but since this involves unexported behaviour in time, there's no guarantee that I can make something reasonable.