[javascript mode] Fix a bug in parsing of arrow function with no args
[javascript mode] Fix a bug in parsing of arrow function with no args

Closes #4131

jkaplon/CodeMirror,mtaran-google/CodeMirror,grzegorzmazur/CodeMirror,mizchi/CodeMirror,wingify/CodeMirror,wingify/CodeMirror,crazy4chrissi/CodeMirror,ejgallego/CodeMirror,thomasjm/CodeMirror,schanzer/CodeMirror,kerabromsmu/CodeMirror,nightwing/CodeMirror,ejgallego/CodeMirror,notepadqq/CodeMirror,kerabromsmu/CodeMirror,alur/CodeMirror,crazy4chrissi/CodeMirror,INTELOGIE/CodeMirror,dperetti/CodeMirror,rrandom/CodeMirror,grzegorzmazur/CodeMirror,INTELOGIE/CodeMirror,codio/CodeMirror,SidPresse/CodeMirror,kerabromsmu/CodeMirror,mizchi/CodeMirror,schanzer/CodeMirror,pabloferz/CodeMirror,dperetti/CodeMirror,codio/CodeMirror,mtaran-google/CodeMirror,notepadqq/CodeMirror,pabloferz/CodeMirror,jayaprabhakar/CodeMirror,INTELOGIE/CodeMirror,sourcelair/CodeMirror,codio/CodeMirror,alur/CodeMirror,jkaplon/CodeMirror,dperetti/CodeMirror,MarcelGerber/CodeMirror,hackmdio/CodeMirror,xeronith/CodeMirror,ficristo/CodeMirror,adobe/CodeMirror2,grzegorzmazur/CodeMirror,hackmdio/CodeMirror,jayaprabhakar/CodeMirror,nightwing/CodeMirror,TDaglis/CodeMirror,TDaglis/CodeMirror,namin/CodeMirror,SidPresse/CodeMirror,xeronith/CodeMirror,crazy4chrissi/CodeMirror,MarcelGerber/CodeMirror,sourcelair/CodeMirror,ficristo/CodeMirror,thomasjm/CodeMirror,wingify/CodeMirror,schanzer/CodeMirror,SidPresse/CodeMirror,ejgallego/CodeMirror,adobe/CodeMirror2,TDaglis/CodeMirror,rrandom/CodeMirror,ficristo/CodeMirror,thomasjm/CodeMirror,namin/CodeMirror,mizchi/CodeMirror,adobe/CodeMirror2,jayaprabhakar/CodeMirror,namin/CodeMirror,rrandom/CodeMirror,mtaran-google/CodeMirror,pabloferz/CodeMirror,notepadqq/CodeMirror,alur/CodeMirror,xeronith/CodeMirror,hackmdio/CodeMirror,MarcelGerber/CodeMirror,sourcelair/CodeMirror,nightwing/CodeMirror,jkaplon/CodeMirror