Remove repeated parameters in fixMangledMediaType

[1]

Hi,

Function fixMangledMediaType from header.go does not remove repeated parameters in some situations.

For example from this line

text/html;charset=UTF-8; charset=UTF-8

because space is not present before first charset.

You can fix this by changing:

			pair := strings.SplitAfter(p, "=")
			if strings.Contains(mtype, pair[0]) {
				// Ignore repeated parameters.
				continue
			}

to this

			pair := strings.SplitAfter(p, "=")
			if strings.Contains(mtype, strings.TrimSpace(pair[0])) {
				// Ignore repeated parameters.
				continue
			}

Thanks.

[James Hillyerd]

Hey man, not trying to be rude, but you are using GitHub wrong. There is an editor built in, and sending a PR will automatically run our unit tests, so you can do all of this without even having a Go development environment. I just created #163 using that method to make sure it works.