Fix missing optional modifier in exp separator

Author: vieira

syntax/javascript.vim

@@ -54,7 +54,7 @@ syntax match   jsModuleComma        contained /,/ skipwhite skipempty nextgroup=
 syntax region  jsString           start=+\z(["']\)+  skip=+\\\%(\z1\|$\)+  end=+\z1+ end=+$+  contains=jsSpecial extend
 syntax region  jsTemplateString   start=+`+  skip=+\\`+  end=+`+     contains=jsTemplateExpression,jsSpecial extend
 syntax match   jsTaggedTemplate   /\<\K\k*\ze`/ nextgroup=jsTemplateString
-syntax match   jsNumber           /\c\<\%(\d\+\%(_\d\+\)\=\%(e[+-]\=\d\+\%(_\d\+\)\)\=\)n\=\>/
+syntax match   jsNumber           /\c\<\%(\d\+\%(_\d\+\)\=\%(e[+-]\=\d\+\%(_\d\+\)\=\)\=\)n\=\>/
 syntax match   jsNumber           /\c\<\%(0b[01]\+\%(_[01]\+\)\=\)\n\=\>/
 syntax match   jsNumber           /\c\<\%(0o\o\+\%(_\o\+\)\=\)n\=\>/
 syntax match   jsNumber           /\c\<\%(0x\x\+\%(_\x\+\)\=\)n\=\>/