Add Bitrise CI support

[gaborszakacs]

Available environment variables: https://devcenter.bitrise.io/faq/available-environment-variables/

[codecov[bot]]

Codecov Report

Merging #31 into master will decrease coverage by 3.57%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master      #31      +/-   ##
==========================================
- Coverage   86.41%   82.84%   -3.58%     
==========================================
  Files           1        1              
  Lines         162      169       +7     
==========================================
  Hits          140      140              
- Misses         22       29       +7

Impacted Files	Coverage Δ
lib/codecov.rb	82.84% <0%> (-3.58%)	:arrow_down:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 72a9f27...77aba04. Read the comment docs.

[codecov-io]

Codecov Report

Merging #31 into master will increase coverage by 0.12%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #31      +/-   ##
==========================================
+ Coverage   96.42%   96.55%   +0.12%     
==========================================
  Files           1        1              
  Lines         252      261       +9     
==========================================
+ Hits          243      252       +9     
  Misses          9        9

Impacted Files	Coverage Δ
lib/codecov.rb	96.55% <100%> (+0.12%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 984d796...b308627. Read the comment docs.

[gaborszakacs]

@hootener I've updated this to the latest, can you pls take a look at that? We are using this at Bitrise on our own projects for a while now.