Allow spaces before lambda.

[anntzer]

Currently, pycodestyle allows

{
    "key":        1,
    "longer-key": 2,
}

(actually it emits a E241 "multiple spaces after ":", but that's suppressed by default) but disallows

{
    "key":        lambda: 1,
    "longer-key": lambda: 2,
}

because the first entry has "multiple spaces before keyword" (before the lambda), even though the cases are clearly similar.

Fix that by excluding lambda from that check.