Fix accessing this.$refs.foo if component is declared with ref="foo"

[msaelices]

Fix #543

[codecov-io]

Codecov Report

Merging #544 into master will increase coverage by 0.03%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #544      +/-   ##
==========================================
+ Coverage   13.64%   13.67%   +0.03%     
==========================================
  Files          49       49              
  Lines        1246     1243       -3     
  Branches      308      308              
==========================================
  Hits          170      170              
+ Misses        844      841       -3     
  Partials      232      232

Impacted Files	Coverage Δ
platform/nativescript/runtime/components/frame.js	0% <0%> (ø)	⬆️

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