Fix multiline arrow function argument syntax

Author: kamikat

syntax/javascript.vim

@@ -170,7 +170,7 @@ syntax keyword jsForAwait             contained await skipwhite skipempty nextgr
 " Matches a single keyword argument with no parens
 syntax match   jsArrowFuncArgs  /\<\K\k*\ze\s*=>/ skipwhite contains=jsFuncArgs skipwhite skipempty nextgroup=jsArrowFunction extend
 " Matches a series of arguments surrounded in parens
-syntax match   jsArrowFuncArgs  /([^()]*)\ze\s*=>/ contains=jsFuncArgs skipempty skipwhite nextgroup=jsArrowFunction extend
+syntax match   jsArrowFuncArgs  /(\_[^()]*\(\_[^()]*(\_[^()]*)\_[^()]*\)*)\ze\s*=>/ contains=jsFuncArgs skipempty skipwhite nextgroup=jsArrowFunction extend
 
 exe 'syntax match jsFunction /\<function\>/      skipwhite skipempty nextgroup=jsGenerator,jsFuncName,jsFuncArgs,jsFlowFunctionGroup skipwhite '.(exists('g:javascript_conceal_function') ? 'conceal cchar='.g:javascript_conceal_function : '')
 exe 'syntax match jsArrowFunction /=>/           skipwhite skipempty nextgroup=jsFuncBlock,jsCommentFunction '.(exists('g:javascript_conceal_arrow_function') ? 'conceal cchar='.g:javascript_conceal_arrow_function : '')