encoding/base64, html/template: fix grammar mistakes

Replace 'does not contains' with 'does not contain' where it appears
in the source code.

Change-Id: Ie7266347c429512c8a41a7e19142afca7ead3922
Reviewed-on: https://go-review.googlesource.com/37887Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/encoding/base64/base64.go

@@ -35,7 +35,7 @@ const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz012345678
 const encodeURL = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
 
 // NewEncoding returns a new padded Encoding defined by the given alphabet,
-// which must be a 64-byte string that does not contains the padding character
+// which must be a 64-byte string that does not contain the padding character
 // or CR / LF ('\r', '\n').
 // The resulting Encoding uses the default padding character ('='),
 // which may be changed or disabled via WithPadding.

src/html/template/escape_test.go

@@ -359,7 +359,7 @@ func TestEscape(t *testing.T) {
 		{
 			"styleStrEncodedProtocolEncoded",
 			`<a style="background: '{{"javascript\\3a alert(1337)"}}'">`,
-			// The CSS string 'javascript\\3a alert(1337)' does not contains a colon.
+			// The CSS string 'javascript\\3a alert(1337)' does not contain a colon.
 			`<a style="background: 'javascript\\3a alert\28 1337\29 '">`,
 		},
 		{