DEV: pin pycifrw to 4.2.1 in Linux travis test.

Avoid SyntaxError that happens for PyCifRW 4.3 with Python 2.7.3.
TODO: revert after next working release of PyCifRW.

Author: pavoljuhas

.travis.yml

@@ -80,6 +80,7 @@ install:
   - $NOMC || conda install --yes --use-local --file=/tmp/mypackage.txt
 
   - $NOAPT || pip install $MYPIPFLAGS coverage
+  - $NOAPT || pip install $MYPIPFLAGS "pycifrw==4.2.1"
   - $NOAPT || easy_install --user "${MYTARBUNDLE}"
 
   # We need to capitalize MYNAME to match Python module name.