bump to cassandra 2.1.5

.travis.yml

@@ -15,8 +15,8 @@ env:
   matrix:
     - CASS=1.2.19 AUTH=false
     - CASS=2.0.14 AUTH=false
-    - CASS=2.1.4  AUTH=false
-    - CASS=2.1.4  AUTH=true
+    - CASS=2.1.5  AUTH=false
+    - CASS=2.1.5  AUTH=true
 
 go:
   - 1.3

README.md

@@ -22,7 +22,7 @@ Supported Versions
 
 The following matrix shows the versions of Go and Cassandra that are tested with the integration test suite as part of the CI build:
 
-Go/Cassandra | 1.2.19 | 2.0.14 | 2.1.4
+Go/Cassandra | 1.2.19 | 2.0.14 | 2.1.5
 -------------| -------| ------| ---------
 1.3  | yes | yes | yes
 1.4  | yes | yes | yes