Update parso to v0.2

[lqmanh]

When trying to run pyls --help, I encountered this error:

pkg_resources.DistributionNotFound: The 'parso==0.1.1' distribution was not found and is required by jedi

However, I already have parso 0.2.0 installed in my system.

[gatesn]

@lqmanh as per this PR davidhalter/jedi@bcd05f5, parso should be compatible with 0.2 as of python-language-server==0.17.2

[gatesn]

Sorry, I read this wrong. We need to fix #334 for pyls to be compatible with parso >= 0.2