[travis] added retries for installing conda, as it seemed to fail on 404 errors

.travis.yml

@@ -43,7 +43,13 @@ before_install:
   - export PATH="$MINICONDA_INSTALL/bin:$PATH";
 
 install:
-  - conda install --yes python=$PYTHON_VERSION numpy=1.9 scipy=0.16 nose pip six matplotlib sphinx;
+  - n=0
+    until [ $n -ge 5 ]
+    do # Retry 5 times, as weird 404 errors seem to popup...
+      conda install --yes python=$PYTHON_VERSION numpy=1.9 scipy=0.16 nose pip six matplotlib sphinx && break
+      n=$[$n+1]
+      sleep 15
+    done
   - pip install codecov
   - pip install pypandoc
   - python setup.py develop