Remove pypy3 from Travis

The new version of pip won't support Python 3.2
and we will need to tweak our .travis.yml and
tox.ini in order to run tests on PyPy 3.

However, since we already removed Python 3.2
from Travis, I decided to remove PyPy 3 as well
(it still targets Python 3.2)

.travis.yml

@@ -7,7 +7,6 @@ env:
   - TOXENV=py34
   - TOXENV=py35
   - TOXENV=pypy
-  - TOXENV=pypy3
 install: pip install tox
 script: tox
 cache:

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py26, py27, py34, py35, pypy, pypy3
+envlist = py26, py27, py34, py35, pypy
 skipsdist = True
 
 [testenv]
@@ -8,5 +8,5 @@ commands = py.test {posargs:tests/} --assert=plain
 deps =
   -rrequirements_test.txt
   py26: unittest2
-  py2{6,7},pypy,py32,pypy3: mock
+  py2{6,7},pypy: mock
   py3{3,4}: aiohttp