Update Travis CI matrix

[kevin-brown]

• Remove sudo from Python 3.7 builds
• Test on Python 3.4

[alvations]

@kevin-brown Thanks for the contribution!

I think py3.4 was purposely dropped to minimize tests and also encourage people to move on to newer Python3 versions. Could you revise your commits and remove the Py3.4 tests?

[kevin-brown]

I added Python 3.4 to the testing matrix because it looks like NLTK officially supports Python 3.4. While I'm in favor of removing it if it's no longer supported, we should probably also remove it from the other places where it is referenced:

• nltk/setup.py

  Line 54 in 3993430

  natural language processing. NLTK requires Python 2.7, 3.4, 3.5, 3.6, or 3.7.""",

• nltk/setup.py

  Line 83 in 3993430

  'Programming Language :: Python :: 3.4',

• nltk/web/install.rst

  Line 4 in 3993430

  NLTK requires Python versions 2.7, 3.4, 3.5, 3.6, or 3.7

Otherwise I'm hesitant to recommend that we don't test on Python 3.4 when it's a version of Python that NLTK claims to officially support.

[alvations]

@stevenbird could we drop support for Python 3.4? If so, @kevin-brown do you mind removing that from the setup.py and install.rst?

[stevenbird]

@kevin-brown: ready for you to drop the change concerning Python 3.4 from your PR

[kevin-brown]

Sorry for the delay. I dropped Python 3.4 so now it's just the changes to the Python 3.7 builds.

[alvations]

Removing sudo from Travis =)

[stevenbird]

Thanks @kevin-brown, @alvations