Update GoSublime-Go.tmLanguage

[mwf]

I've fixed explicit argument indexes according to current spec https://golang.org/pkg/fmt/

Format is now highlighted when using indexes [n] in different cases.
Please, check the syntax highlighting for:

fmt.Printf("\nfoo %[1]s %[1]s", "bar")
fmt.Printf("\n%d %d %#[1]x %#x", 16, 17)
fmt.Printf("\n%#20[2]x %+#20[1]x", 16, 17)
fmt.Printf("\n%[3]*.[2]*[1]f", 12.0, 2, 6)
fmt.Printf("\n%6.2f", 12.0)
fmt.Printf("\n%*.*f", 6, 2, 12.0)

I wanted to know what should I do with GoSublime-Go.tmLanguage.json - this file seems to be redundant and autogenerated somehow. If it's not used by Sublime itself why do you need it?