[travis] Set pyyaml version on osx build

mpsonntag · mpsonntag · commit aaae2e2fc34e · 2019-02-13T17:03:53.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -53,7 +53,7 @@ install:
       export PIPCMD=pip;
     fi;
 
-  - $PIPCMD install lxml enum34 pyyaml rdflib
+  - $PIPCMD install lxml enum34 pyyaml==4.2b4 rdflib
 
 script:
   - which $PYCMD
