Unable to parse stub conditionals

[tharvik]

In PEP 484, there is a section on conditional stubs.

For example, the next code is a valid stub code

import sys

if sys.version_info <= (3,):
    def old_code_stub() -> None: ...

But currently, running pytd on it will fail with

Error while parsing pyi:

  File "/tmp/asd.py", line 3
    if sys.version_info <= (3,):
          ^
SyntaxError: Unexpected 'DOT'

Found while doing typeshed#345.

[matthiaskramm]

Fixed.