Update .travis.yml

.travis.yml

@@ -35,7 +35,7 @@ before_install:
   - export PATH="$DOTNET_INSTALL_DIR:$PATH"  
   
 install:
-  - travis_retry curl -sSL https://raw.githubusercontent.com/dotnet/cli/rel/1.0.0/scripts/obtain/dotnet-install.sh | bash /dev/stdin --version "$CLI_VERSION" --install-dir "$DOTNET_INSTALL_DIR"
+  - travis_retry curl -sSL https://raw.githubusercontent.com/dotnet/cli/rel/1.0.0/scripts/obtain/dotnet-install.sh | bash /dev/stdin --channel 2.0 --version "$CLI_VERSION" --install-dir "$DOTNET_INSTALL_DIR"
 
 #cache: 
 # - apt