urllib3 uses pytest now, various upgrades to the travis env (#634)

* urllib3 uses pytest now, also use trusty

* more improvements

* keep modernizing

* try trusty later.

* revert

* still try for trusty, back to the right pypy
diff --git a/.travis.yml b/.travis.yml
index 38324ee..f37148c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,3 +1,4 @@
+dist: trusty
 sudo: false
 language: python
 
@@ -31,8 +32,7 @@
     env: TOXENV=py35
   - python: "3.6"
     env: TOXENV=py36
-  - python: "pypy"
-    env: TOXENV=pypy
+  - env: TOXENV=pypy
 
   # Also run the tests against cryptography master.
   - python: "2.6"
@@ -47,8 +47,7 @@
     env: TOXENV=py35-cryptographyMaster
   - python: "3.6"
     env: TOXENV=py36-cryptographyMaster
-  - python: "pypy"
-    env: TOXENV=pypy-cryptographyMaster
+  - env: TOXENV=pypy-cryptographyMaster
 
   # And current minimum cryptography version.
   - python: "2.6"
@@ -63,8 +62,7 @@
     env: TOXENV=py35-cryptographyMinimum
   - python: "3.6"
     env: TOXENV=py36-cryptographyMinimum
-  - python: "pypy"
-    env: TOXENV=pypy-cryptographyMinimum
+  - env: TOXENV=pypy-cryptographyMinimum
 
 
   # Make sure we don't break Twisted or urllib3
@@ -113,7 +111,8 @@
     else
       # install our own pypy. This can be removed if and when Travis gets a reasonably up to date pypy
       if [[ "${TOXENV}" = pypy* ]]; then
-          git clone https://github.com/yyuu/pyenv.git ~/.pyenv
+          rm -rf ~/.pyenv
+          git clone --depth=1 https://github.com/yyuu/pyenv.git ~/.pyenv
           PYENV_ROOT="$HOME/.pyenv"
           PATH="$PYENV_ROOT/bin:$PATH"
           eval "$(pyenv init -)"
@@ -129,7 +128,6 @@
   - |
     if [[ "$(uname -s)" == 'Darwin' ]]; then
       # set our flags to use homebrew openssl
-      export ARCHFLAGS="-arch x86_64"
       if [[ "${OPENSSL}"  == "1.1.0" ]]; then
         export LDFLAGS="-L/usr/local/opt/openssl@1.1/lib"
         export CFLAGS="-I/usr/local/opt/openssl@1.1/include"
diff --git a/tox.ini b/tox.ini
index 723562e..1141261 100644
--- a/tox.ini
+++ b/tox.ini
@@ -44,7 +44,7 @@
     python -c "import OpenSSL.SSL; print(OpenSSL.SSL.SSLeay_version(OpenSSL.SSL.SSLEAY_VERSION))"
     python -c "import cryptography; print(cryptography.__version__)"
     {toxinidir}/.travis/install_urllib3.sh
-    nosetests urllib3/test
+    pytest urllib3/test
     rm -rf ./urllib3
 
 [testenv:flake8]