Auto merge of #2584 - mikeperri:typescript-diagnostics, r=micbou

Typescript diagnostics

# PR Prelude

Thank you for working on YCM! :)

**Please complete these steps and check these boxes (by putting an `x` inside
the brackets) _before_ filing your PR:**

- [x] I have read and understood YCM's [CONTRIBUTING][cont] document.
- [x] I have read and understood YCM's [CODE_OF_CONDUCT][code] document.
- [x] I have included tests for the changes in my PR. If not, I have included a
  rationale for why I haven't.
- [x] **I understand my PR may be closed if it becomes obvious I didn't
  actually perform all of these steps.**

# Why this change is necessary and useful
This just makes use of [these changes](ycm-core/ycmd#718) to ycmd.
It adds TypeScript to the list of filetypes that diagnostics are supported for and reflects that in the README. (And updates ycmd.)
No tests are included, since the only code that changed is the hard-coded list of filetypes. The new ycmd functionality is tested in that project.

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README.md

@@ -729,6 +729,7 @@ Quick Feature Summary
 ### TypeScript
 
 * Semantic auto-completion
+* Real-time diagnostic display
 * Renaming symbols (`RefactorRename <new name>`)
 * Go to definition, find references (`GoToDefinition`, `GoToReferences`)
 * Semantic type information for identifiers (`GetType`)
@@ -1131,9 +1132,10 @@ Completer API.
 ### Diagnostic Display
 
 YCM will display diagnostic notifications for C-family and C# languages if you
-compiled YCM with Clang and Omnisharp support, respectively. Since YCM continuously
-recompiles your file as you type, you'll get notified of errors and warnings
-in your file as fast as possible.
+compiled YCM with Clang and Omnisharp support, respectively. Diagnostics will
+also be displayed for TypeScript. Since YCM continuously recompiles your file as
+you type, you'll get notified of errors and warnings in your file as fast as
+possible.
 
 Here are the various pieces of the diagnostic UI:
 

python/ycm/youcompleteme.py

@@ -100,7 +100,8 @@ def PatchNoProxy():
   'YCM core library too old; PLEASE RECOMPILE by running the install.py '
   'script. See the documentation for more details.' )
 SERVER_IDLE_SUICIDE_SECONDS = 10800  # 3 hours
-DIAGNOSTIC_UI_FILETYPES = set( [ 'cpp', 'cs', 'c', 'objc', 'objcpp' ] )
+DIAGNOSTIC_UI_FILETYPES = set( [ 'cpp', 'cs', 'c', 'objc', 'objcpp',
+                                 'typescript' ] )
 CLIENT_LOGFILE_FORMAT = 'ycm_'
 SERVER_LOGFILE_FORMAT = 'ycmd_{port}_{std}_'