SwiftLint2

rewrite FunctionBodyLengthRuleTests to compile 500x faster

before:
  10828.9ms @objc func testFunctionBodyLengthsWithComments()
  10250.3ms @objc func testFunctionBodyLengthsWithMultilineComments()
  1236.7ms  @objc func testFunctionBodyLengths()

after:
  18.5ms @objc func testFunctionBodyLengths()
  16.0ms private func funcWithBody(body: String) -> String
  6.5ms  @objc func testFunctionBodyLengthsWithMultilineComments()
  5.7ms  @objc func testFunctionBodyLengthsWithComments()