Mark "do" as being beforeExpr
Mark "do" as being beforeExpr

Fixes #320.

happibum/acorn,ajaxorg/acorn,TimothyGu/acorn,marijnh/acorn,marijnh/acorn,mathiasbynens/acorn,mathiasbynens/acorn,mathiasbynens/acorn,MarcelGerber/acorn,Rich-Harris/acorn,Rich-Harris/acorn,btmills/acorn,btmills/acorn,Rich-Harris/acorn,ajaxorg/acorn,mysticatea/acorn,ternjs/acorn,happibum/acorn,MarcelGerber/acorn,ajaxorg/acorn,TimothyGu/acorn,TimothyGu/acorn,marijnh/acorn,happibum/acorn,mysticatea/acorn,btmills/acorn,ternjs/acorn,ternjs/acorn,mysticatea/acorn,MarcelGerber/acorn