Parenthesis color mismatch

same as #56 but more description,

I have the same issue, using 
git@github.com:luochen1990/rainbow.git plugin at current latest hash: 18b7bc1 is:
to replicate I have a new file with a content:
`[].map(function(a,b){ })`
you will see the parenthesis has shifted color right after "b",
everything inside the curly braces is fine, except if you have another
function passed as a parameter
