[Pubsub] Fix entrypoint

[anovis]

set entrypoint to goblet_entrypoint instead of app because of #88 (closes #95)

[codecov]

Codecov Report

Merging #97 (18b0107) into master (94f1944) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #97   +/-   ##
=======================================
  Coverage   88.99%   88.99%           
=======================================
  Files          25       25           
  Lines        1726     1726           
=======================================
  Hits         1536     1536           
  Misses        190      190           

Impacted Files	Coverage Δ
goblet/decorators.py	87.03% <100.00%> (ø)

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