Update .travis.yml to use the latest Rubies and Cassandra

Author: kishkaru

.travis.yml

@@ -12,8 +12,8 @@ before_install:
 rvm:
   - 1.9.3
   - 2.0.0
-  - 2.1.5
-  - 2.2.0
+  - 2.1.6
+  - 2.2.2
   - jruby
   - rbx-2.2.10
 jdk:
@@ -23,12 +23,12 @@ env:
     - FAIL_FAST=no
     - COVERAGE=no
   matrix:
-    - CASSANDRA_VERSION=2.1.3 TEST_SUITE=rspec
-    - CASSANDRA_VERSION=2.1.3 TEST_SUITE=integration
-    - CASSANDRA_VERSION=2.1.3 TEST_SUITE=cucumber
-    - CASSANDRA_VERSION=2.0.12 TEST_SUITE=rspec
-    - CASSANDRA_VERSION=2.0.12 TEST_SUITE=integration
-    - CASSANDRA_VERSION=2.0.12 TEST_SUITE=cucumber
+    - CASSANDRA_VERSION=2.1.6 TEST_SUITE=rspec
+    - CASSANDRA_VERSION=2.1.6 TEST_SUITE=integration
+    - CASSANDRA_VERSION=2.1.6 TEST_SUITE=cucumber
+    - CASSANDRA_VERSION=2.0.15 TEST_SUITE=rspec
+    - CASSANDRA_VERSION=2.0.15 TEST_SUITE=integration
+    - CASSANDRA_VERSION=2.0.15 TEST_SUITE=cucumber
     - CASSANDRA_VERSION=1.2.19 TEST_SUITE=rspec
     - CASSANDRA_VERSION=1.2.19 TEST_SUITE=integration
     - CASSANDRA_VERSION=1.2.19 TEST_SUITE=cucumber