prepare travis for python3 testing

.travis.yml

@@ -58,9 +58,9 @@ install:
   - export CC=${CC}-${COMPILER_VERSION}
 
   - if [ "${PYTHON_VERSION}" = "3" ]; then
-      export PIP=pip3
+      export PIP=pip3;
     else
-      export PIP=pip
+      export PIP=pip;
     fi
 
   - BOOST_VERSION=1.65.0 # match version number of cache directory above