Bump version to 3.0

[richin13]

Fix #322

[codecov-commenter]

Codecov Report

Merging #323 (71a3415) into master (57cd786) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #323   +/-   ##
=======================================
  Coverage   96.91%   96.91%           
=======================================
  Files           9        9           
  Lines         616      616           
=======================================
  Hits          597      597           
  Misses         19       19           

Impacted Files	Coverage Δ
graphene_sqlalchemy/__init__.py	100.00% <100.00%> (ø)

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[erikwrede]

Closing this for now; the plan is to release additional betas to incrementally add (breaking) changes & new features. Full "non-beta" release will take place afterwards.