update regexes to not match wrong keys

Consider this yaml snippet:

    url: http://www.example.com

With your current regexes the `http:` gets highlighted as a yamlKey and yamlDelimiter. 

Quoting [Wikipedia](http://en.wikipedia.org/wiki/YAML#Syntax): **YAML requires that colons** and commas used as list separators **be followed by a space** so that scalar values containing embedded punctuation (such as 5,280 or http://www.wikipedia.org) can generally be represented without needing to be enclosed in quotes.

So the `http:` shouldn't be highlighted because there is no space following the colon. I updated your regexes for yamlKeys and yamlDelimiters to only match if there's a space or newline following.

Oh and the yamlKey regex seems to get definet twice in yaml.vim. You might want to remove the first definition.