Pin dotnet-nightly package on Travis

.travis.yml

@@ -9,7 +9,7 @@ before_install:
   - sudo sh -c 'echo "deb [arch=amd64] http://apt-mo.trafficmanager.net/repos/dotnet/ trusty main" > /etc/apt/sources.list.d/dotnetdev.list'
   - sudo apt-key adv --keyserver apt-mo.trafficmanager.net --recv-keys 417A0893
   - sudo apt-get -qq update
-  - sudo apt-get install -y dotnet-nightly
+  - sudo apt-get install -y dotnet-nightly=1.0.1.001252-1
 script:
   - dotnet restore
   - ./build.sh