.travis/install.sh: simplify; drop jython; don't use pyenv on Linux, use default Travis pypy

Since tox already creates its own test environment, so there's no need to create another virtual environment to install tox into.
This simplifies things a bit.

.travis/install.sh

@@ -3,6 +3,9 @@
 set -e
 set -x
 
+pip_options="--upgrade"
+ci_requirements="pip setuptools tox"
+
 if [[ "$(uname -s)" == 'Darwin' ]]; then
     # install pyenv from the git repo (quicker than using brew)
     git clone https://github.com/yyuu/pyenv.git ~/.pyenv
@@ -16,50 +19,18 @@ if [[ "$(uname -s)" == 'Darwin' ]]; then
             curl -O https://bootstrap.pypa.io/get-pip.py
             python get-pip.py --user
             ;;
-        py34)
-            pyenv install 3.4.5
-            pyenv global 3.4.5
-            ;;
         py35)
             pyenv install 3.5.2
             pyenv global 3.5.2
             ;;
-        pypy)
-            pyenv install pypy-5.4.1
-            pyenv global pypy-5.4.1
-            ;;
     esac
     pyenv rehash
-    python -m pip install --user --upgrade pip virtualenv
+
+    # add --user option so we don't require sudo
+    pip_options="$pip_options --user"
 else
-    # on Linux, we only need pyenv to get the latest pypy and jython
-    if [[ "${TOXENV}" == "pypy" || "${TOXENV}" == "jython" ]]; then
-        git clone https://github.com/yyuu/pyenv.git ~/.pyenv
-        PYENV_ROOT="$HOME/.pyenv"
-        PATH="$PYENV_ROOT/bin:$PATH"
-        eval "$(pyenv init -)"
-
-        if [[ "${TOXENV}" == "pypy" ]]; then
-            pyenv install pypy-5.4.1
-            pyenv global pypy-5.4.1
-        else
-            pyenv install jython-2.7.1b3
-            pyenv global jython-2.7.1b3
-        fi
-        pyenv rehash
-    fi
-    if [[ "${TOXENV}" == "jython" ]]; then
-        # for jython we just run pytest for now, without virtualenv nor tox.
-        # See: https://github.com/behdad/fonttools/issues/575
-        jython -m pip install pytest
-    else
-        pip install --upgrade pip virtualenv
-    fi
+    # on Linux, we're already in a virtualenv; no --user required
+    :
 fi
 
-if [[ "${TOXENV}" != "jython" ]]; then
-    # activate virtualenv and install test requirements
-    python -m virtualenv ~/.venv
-    source ~/.venv/bin/activate
-    pip install -r dev-requirements.txt
-fi
+python -m pip install $pip_options $ci_requirements