Moved requirements_parser to core-requirements.txt

[christopherbunn]

Fixed an issue where requirements_parser is not installed as a core dependency.

[dsherry]

Super fast, thank you!

Backstory: I added requirements-parser as a dep for some test code a while back, and added it to test-requirements.txt. Then #300 added it as a core requirement but we forgot to get it into core-requirements.txt, and our test env installs both so there'd be no way to know that from the checkin tests.

I wonder what, if anything, we can do to avoid this in the future. Perhaps we need a smoke test which just installs core-requirements.txt and then tries to do a limited set of stuff. Or perhaps simply having the perf tests serves as that smoke test. Or, we don't need to do anything, because the chances of this situation happening again are low, i.e. forgetting to move an existing test req to core reqs.

In any case, thanks for getting this PR up!

[dsherry]

@christopherbunn please move this to Review/QA

[codecov]

Codecov Report

Merging #673 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #673   +/-   ##
=======================================
  Coverage   99.06%   99.06%           
=======================================
  Files         139      139           
  Lines        4907     4907           
=======================================
  Hits         4861     4861           
  Misses         46       46           

Impacted Files	Coverage Δ
evalml/tests/utils_tests/test_cli_utils.py	100.00% <100.00%> (ø)

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