Increase .travis.yml consistency between repos - aspnet/Universe#349 - minimize `dotnet` setup time; no need for caching - `KOREBUILD_TEST_DNXCORE` env variable isn't used anymore - no need for icu4c w/ current `dotnet` builds
Increase .travis.yml consistency between repos
- aspnet/Universe#349
- minimize `dotnet` setup time; no need for caching
- `KOREBUILD_TEST_DNXCORE` env variable isn't used anymore
- no need for icu4c w/ current `dotnet` builds

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