Allow newer versions of several requirements

[mbarrien]

signxml is pinning the max version of several requirements of libraries that have all updated past the max version. This PR upgrades them all.

For a library used in other projects, it may be advisable to remove the max version and let the library user themselves manage the max versions in their own requirements files (and let the library user deal with the conflicts themselves; they're smart enough to figure it out). This will get rid of the need for the PR every time a library upgrades in backwards compatible ways.

[codecov-io]

Codecov Report

Merging #84 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #84   +/-   ##
=======================================
  Coverage   95.32%   95.32%           
=======================================
  Files           3        3           
  Lines         599      599           
=======================================
  Hits          571      571           
  Misses         28       28

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[kislyuk]

Yes, I think this is a tricky question that ultimately relates to whether the maintainer should do the due diligence of testing before indicating that the new dependency version is safe to use with the maintainer's library (here I'm interpreting major version numbers per the semver standard) or let stuff potentially break and rely on users to sort it out.

[kislyuk]

See 6529b68. If you want to make the pyasn1 dependency explicit, please open another PR.