fmt: fix an error in documentation for fmt

Original Printf("%d", hi) obviously doesn't produce
%!d(string=hi) unless somewhere before this code
block you have hi := "hi" somewhere, also this change
maintains consistency with the rest of it

Change-Id: I40d8cca623176dcad66374ba74e3a1f8f975ac9e
GitHub-Last-Rev: 242e9ee6afba7ab22ed2967b0ba01ef18db01ca9
GitHub-Pull-Request: golang/go#30223
Reviewed-on: https://go-review.googlesource.com/c/162541Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/fmt/doc.go

@@ -217,7 +217,7 @@
 	description of the problem, as in these examples:
 
 		Wrong type or unknown verb: %!verb(type=value)
-			Printf("%d", hi):          %!d(string=hi)
+			Printf("%d", "hi"):        %!d(string=hi)
 		Too many arguments: %!(EXTRA type=value)
 			Printf("hi", "guys"):      hi%!(EXTRA string=guys)
 		Too few arguments: %!verb(MISSING)