refac(ci): improve build time

also added testing of mono none in order to force travis to run
unit tests

Author: juancarlostong

.travis.yml

@@ -1,6 +1,8 @@
 language: csharp
 mono:
-- 5.2.0
+  - 5.2.0
+# needed to make travis run the unit tests
+  - none
 solution: "./OptimizelySDK.Travis.sln"
 install:
   - nuget restore ./OptimizelySDK.Travis.sln
@@ -18,7 +20,9 @@ stages:
 jobs:
   include:
     - stage: 'Integration tests'
+      merge_mode: replace
       env: SDK=csharp
+      cache: false
       language: python
       before_install: skip
       install:
@@ -27,4 +31,4 @@ jobs:
         - "aws s3 cp s3://optimizely-travisci-artifacts/ci/trigger_fullstack-sdk-compat.sh ci/ && chmod u+x ci/trigger_fullstack-sdk-compat.sh"
       script:
         - "ci/trigger_fullstack-sdk-compat.sh"
-      after_success: skip
+      after_success: travis_terminate 0