html: fix small typo

LGTM=dsymonds, adg, crawshaw, r, bradfitz, campoy, nigeltao, sameer, iant, robsc, djd, michael.j.fromberger, gmlewis, adonovan, rsc
R=golang-codereviews, dsymonds, adg, crawshaw, r, nigeltao, sameer, iant, robsc, djd, michael.j.fromberger, gmlewis, adonovan, rsc
CC=golang-codereviews
https://golang.org/cl/98880043

src/pkg/html/template/js.go

@@ -99,7 +99,7 @@ func nextJSCtx(s []byte, preceding jsCtx) jsCtx {
 	return jsCtxDivOp
 }
 
-// regexPrecederKeywords is a set of reserved JS keywords that can precede a
+// regexpPrecederKeywords is a set of reserved JS keywords that can precede a
 // regular expression in JS source.
 var regexpPrecederKeywords = map[string]bool{
 	"break":      true,