Fix DeprecationWarning in 3.7

[tirkarthi]

• This PR fixes the deprecation warnings in 3.7
• Upgrade freezegun to support 3.7. Current version is incompatible with 3.7 so I have upgraded it (Reference : 3.7 support (uuid module changes) spulec/freezegun#231)
• Grepping for similar imports doesn't show up any places related to this

Successful build : https://travis-ci.org/tirkarthi/babel/builds/446248386

I added 3.7 but it seems Travis has problems with 3.7 and Ubuntu 14.04 so I have reverted it. Since the CI passes on 3.6 and 2.7 I think it's safe to merge. I cannot verify them locally due to setting up locales and test data in my Ubuntu machine.

Travis issue : travis-ci/travis-ci#9815
Python 3.7 and Ubuntu 14.04 issue : travis-ci/travis-ci#9069

closes#607

Friendly ping @akx

Thanks

[codecov-io]

Codecov Report

Merging #608 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@ Coverage Diff @@## master #608 +/- ##
==========================================
+ Coverage 90.31% 90.31% +<.01% 
==========================================
Files 24 24 Lines 4128 4130 +2 ==========================================
+ Hits 3728 3730 +2 
Misses 400 400

Impacted Files	Coverage Δ
babel/_compat.py	98.14% <100%> (+0.1%)	⬆️
babel/localedata.py	95.41% <100%> (-0.05%)	⬇️

---

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 d2cf189...49b75c4. Read the comment docs.

[tirkarthi]

Closing since #609 was merged