Update CI to cover python 3.7

[utkonos]

This change is 

[coveralls]

Pull Request Test Coverage Report for Build 101

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 95.408%

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Totals
Change from base Build 98:	0.5%
Covered Lines:	187
Relevant Lines:	196

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 101

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.5%) to 95.408%

---

Totals
Change from base Build 98:	0.5%
Covered Lines:	187
Relevant Lines:	196

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 105

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.898%

---

Totals
Change from base Build 98:	0.0%
Covered Lines:	186
Relevant Lines:	196

---

💛 - Coveralls

[martinmr]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @utkonos)

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.travis.yml, line 7 at r1 (raw file):

sudo: required
dist: trusty
matrix:

Why can't we just list 3.7 next to 3.6 and 2.7? Is it because of the ubuntu version?

Also, from the release notes it doesn't look like 3.7 is a big change from 3.6 so it's fine replacing 3.6 with 3.7.

[utkonos]

@martinmr The version of ubuntu is needed for python 3.7 unless you want to install python altinstall for each CI build. I made a minimal change to preserve the python and ubuntu version that you already have for 3.6 and 2.7. It would be great if you just replaced 3.7 for 3.6. Give me a sec and I'll add to this PR with that change and make the ubuntu version uniform.

[martinmr]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @utkonos)

[martinmr]

Looks good. Thanks for your contribution. I am merging it now.