[dotnet] for linux target, bring up to jdk8 since jdk7 no longer available for Trusty; for linux and osx targets, bring up dotnet from 1.0.3 to 1.0.4; Trusty image now has mvn 3.3.9 builtin, removed install code

[xied75]

@ericvergnaud @parrt

[parrt]

I'll wait for @ericvergnaud to review. thanks!

[ericvergnaud]

Linux build is fixed, but OS X one is now broken, see
https://travis-ci.org/antlr/antlr4/builds/247122557?utm_source=github_status&utm_medium=notification

[xied75]

It worked for my own push here https://travis-ci.org/xied75/antlr4/builds/247077570
The problem looks like transient random OSX image issues I guess. See the other two failures on OSX, try a restart?

[ericvergnaud]

3 restarts all failed, but Travis seems in very bas state tonight, especially the OSX builds
plus GitHub is also not doing its job
let's retry tomorrow

[ericvergnaud]

Indeed, Travis is flaky, relaunching the build works
@parrt blessed