chore: update to TypeScript 3

[seanf]

https://blogs.msdn.microsoft.com/typescript/2018/07/30/announcing-typescript-3-0/

Checklist

• JIRA link
• Check target branch
• Make sure all commit statuses are green or otherwise documented reasons to ignore
• QA needs to evaluate against the JIRA ticket
• Changed files and commits make sense for this PR

See Zanata Development Guidelines more for information.

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This template can be updated in .github/PULL_REQUEST_TEMPLATE.md

[zubot]

This change is 

[codecov]

Codecov Report

Merging #1022 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1022      +/-   ##
============================================
+ Coverage     36.82%   36.88%   +0.05%     
- Complexity     6128     6177      +49     
============================================
  Files          1649     1649              
  Lines         65356    65638     +282     
  Branches       7615     7649      +34     
============================================
+ Hits          24070    24209     +139     
- Misses        39189    39328     +139     
- Partials       2097     2101       +4

Impacted Files	Coverage Δ	Complexity Δ
...nata/async/handle/MergeTranslationsTaskHandle.java	93.33% <0%> (-6.67%)	7% <0%> (+2%)
...org/zanata/async/handle/CopyVersionTaskHandle.java	52.38% <0%> (-5.96%)	5% <0%> (+1%)
...nd/src/app/editor/reducers/phrase-reducer/index.js	85.62% <0%> (ø)	0% <0%> (ø)	⬇️
...c/main/java/org/zanata/action/DashboardAction.java	0% <0%> (ø)	0% <0%> (ø)	⬇️
...end/src/app/editor/reducers/suggestions-reducer.js	100% <0%> (ø)	0% <0%> (ø)	⬇️
...r/reducers/phrase-reducer/filter-status-reducer.js	100% <0%> (ø)	0% <0%> (ø)	⬇️
.../main/java/org/zanata/action/CopyTransManager.java	0% <0%> (ø)	0% <0%> (ø)	⬇️
...ontend/src/app/editor/reducers/settings-reducer.js	80.45% <0%> (ø)	0% <0%> (ø)	⬇️
...ain/java/org/zanata/action/CopyVersionManager.java	0% <0%> (ø)	0% <0%> (ø)	⬇️
...rc/main/java/org/zanata/async/AsyncTaskHandle.java	65.76% <0%> (+0.05%)	59% <0%> (+19%)	⬆️
... and 8 more

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[djansen-redhat]

Verified, but only to a cursory level