Add support for async and await keywords

Author: wbinnssmith

syntax/javascript.vim

@@ -133,6 +133,7 @@ syntax keyword jsLabel          case default
 syntax keyword jsKeyword        yield
 syntax keyword jsClass          extends class
 syntax keyword jsException      try catch throw finally
+syntax keyword jsAsyncKeyword   async await
 
 syntax keyword jsGlobalObjects   Array Boolean Date Function Iterator Number Object Symbol Map WeakMap Set RegExp String Proxy Promise ParallelArray ArrayBuffer DataView Float32Array Float64Array Int16Array Int32Array Int8Array Uint16Array Uint32Array Uint8Array Uint8ClampedArray Intl JSON Math console document window
 syntax match   jsGlobalObjects  /\%(Intl\.\)\@<=\(Collator\|DateTimeFormat\|NumberFormat\)/
@@ -192,7 +193,7 @@ endif "DOM/HTML/CSS
 "" end DOM/HTML/CSS specified things
 
 "" Code blocks
-syntax cluster jsExpression contains=jsComment,jsLineComment,jsBlockComment,jsTaggedTemplate,jsTemplateString,jsStringD,jsStringS,jsRegexpString,jsNumber,jsFloat,jsThis,jsStatic,jsSuper,jsOperator,jsBooleanTrue,jsBooleanFalse,jsNull,jsFunction,jsArrowFunction,jsGlobalObjects,jsExceptions,jsFutureKeys,jsDomErrNo,jsDomNodeConsts,jsHtmlEvents,jsDotNotation,jsBracket,jsParen,jsBlock,jsFuncCall,jsUndefined,jsNan,jsKeyword,jsStorageClass,jsPrototype,jsBuiltins,jsNoise,jsCommonJS,jsAssignmentExpr,jsImportContainer,jsExportContainer,jsClass,jsArgsObj,jsDecorator
+syntax cluster jsExpression contains=jsComment,jsLineComment,jsBlockComment,jsTaggedTemplate,jsTemplateString,jsStringD,jsStringS,jsRegexpString,jsNumber,jsFloat,jsThis,jsStatic,jsSuper,jsOperator,jsBooleanTrue,jsBooleanFalse,jsNull,jsFunction,jsArrowFunction,jsGlobalObjects,jsExceptions,jsFutureKeys,jsDomErrNo,jsDomNodeConsts,jsHtmlEvents,jsDotNotation,jsBracket,jsParen,jsBlock,jsFuncCall,jsUndefined,jsNan,jsKeyword,jsStorageClass,jsPrototype,jsBuiltins,jsNoise,jsCommonJS,jsAssignmentExpr,jsImportContainer,jsExportContainer,jsClass,jsArgsObj,jsDecorator,jsAsyncKeyword
 syntax cluster jsAll        contains=@jsExpression,jsLabel,jsConditional,jsRepeat,jsReturn,jsStatement,jsTernaryIf,jsException
 syntax region  jsBracket    matchgroup=jsBrackets     start="\[" end="\]" contains=@jsAll,jsParensErrB,jsParensErrC,jsBracket,jsParen,jsBlock,@htmlPreproc fold
 syntax region  jsParen      matchgroup=jsParens       start="("  end=")"  contains=@jsAll,jsOf,jsParensErrA,jsParensErrC,jsParen,jsBracket,jsBlock,@htmlPreproc fold
@@ -267,6 +268,7 @@ if version >= 508 || !exists("did_javascript_syn_inits")
   HiLink jsStatement            Statement
   HiLink jsException            Exception
   HiLink jsKeyword              Keyword
+  HiLink jsAsyncKeyword         Keyword
   HiLink jsArrowFunction        Type
   HiLink jsFunction             Type
   HiLink jsGenerator            jsFunction