FIX: strip extraneous whitespace in trait desc

Some wrapped strings in the description field for Traits were printing very awkwardly in the help display, e.g.:

    [Optional]
    between_loops: (an integer, nipype default value: [5])
		loops used to                                                           realign
		different                                                           runs

This small fix should take care of that problem:

    [Optional]
    between_loops: (an integer, nipype default value: [5])
        loops used to realign different runs