Fixed spelling error in builder/dockerfile/parser/parser.go

Signed-off-by: Tiffany Jernigan <tiffany.f.j@gmail.com>

rewritten from github.com/moby/moby a07c57f656846ee0de67ac4f575fe5b76d482efb

frontend/dockerfile/parser/parser.go

@@ -91,7 +91,7 @@ func init() {
 // ParseLine parse a line and return the remainder.
 func ParseLine(line string) (string, *Node, error) {
 
-	// Handle the parser directive '# escape=<char>. Parser directives must preceed
+	// Handle the parser directive '# escape=<char>. Parser directives must precede
 	// any builder instruction or other comments, and cannot be repeated.
 	if lookingForDirectives {
 		tecMatch := tokenEscapeCommand.FindStringSubmatch(strings.ToLower(line))