docs: remove extra backtick from README.md.tmpl

Fix stale template after golangci#103

Author: jirfag

README.md.tmpl

@@ -271,7 +271,7 @@ required = [
 ```
 In your CI scripts, install the vendored `golangci-lint` like this:
 ```bash
-go install ./vendor/github.com/golangci/golangci-lint/cmd/golangci-lint/`
+go install ./vendor/github.com/golangci/golangci-lint/cmd/golangci-lint/
 ```
 Vendoring `golangci-lint` saves a network request, potentially making your CI system a little more reliable.