fix: Update vue.styl (#634)

CSS style for functions is specified in buble.styl only. Thus, for example, bash commands from prism-bash.js (function section) are not highlighted. You can add a new CSS style with the right color you think fits better  :).

src/themes/vue.styl

@@ -159,7 +159,7 @@ body
 .token.attr-value, .token.control, .token.directive, .token.unit
   color var(--theme-color, $color-primary)
 
-.token.keyword
+.token.keyword, .token.function
   color #e96900
 
 .token.statement, .token.regex, .token.atrule