travis: try using jython 2.7.1b2; don't install from requirements.txt on Jython to avoid RuntimeError

I don't know why but when I `pip install -r requirements.txt` on Jython,
it always raises a Java StackOverflowError.
If I install the deps individually, it works...

$ pip install -v -r dev-requirements.txt
Exception:
Traceback (most recent call last):
  File "fonttools-jy271b2/Lib/site-packages/pip/basecommand.py", line 209, in main
    status = self.run(options, args)
  File "fonttools-jy271b2/Lib/site-packages/pip/commands/install.py", line 285, in run
    self.populate_requirement_set(
  File "fonttools-jy271b2/Lib/site-packages/pip/basecommand.py", line 286, in populate_requirement_set
    for req in parse_requirements(
  File "fonttools-jy271b2/Lib/site-packages/pip/req/req_file.py", line 89, in parse_requirements
    for line_number, line in lines_enum:
  File "fonttools-jy271b2/Lib/site-packages/pip/req/req_file.py", line 323, in ignore_comments
    for line_number, line in lines_enum:
  File "fonttools-jy271b2/Lib/site-packages/pip/req/req_file.py", line 298, in join_lines
    if COMMENT_RE.match(line):
RuntimeError: maximum recursion depth exceeded (Java StackOverflowError)

.travis/install.sh

@@ -47,8 +47,8 @@ else
             pyenv install pypy-5.0.0
             pyenv global pypy-5.0.0
         else
-            pyenv install jython-2.7.0
-            pyenv global jython-2.7.0
+            pyenv install jython-2.7.1b2
+            pyenv global jython-2.7.1b2
         fi
         pyenv rehash
     fi
@@ -58,4 +58,11 @@ fi
 # activate virtualenv and install test requirements
 python -m virtualenv ~/.venv
 source ~/.venv/bin/activate
-pip install -r dev-requirements.txt
+
+if [[ "${TOXENV}" == "jython" ]]; then
+    # using requirements.txt with pip on Jython raises `RuntimeError:
+    # maximum recursion depth exceeded (Java StackOverflowError)`
+    pip install pytest
+else
+    pip install -r dev-requirements.txt
+fi