Remove useless cache folder

fixes TechEmpower/FrameworkBenchmarks#1290

.travis.yml

@@ -164,10 +164,4 @@ install:
 script: 
   # Pick one test in this directory and verify
   - time ./toolset/run-ci.py verify "$TESTDIR"
-
-cache:
-  directories:
-    - installs/mono-3.2.8
-    - installs/py2
-    - installs/py3
-    - installs/perl-5.18
+