Auto merge of #45304 - kennytm:travis-color-color-conflict, r=aturon
Auto merge of #45304 - kennytm:travis-color-color-conflict, r=aturon

Fix rustbuild --color conflict when building on Travis outside of Docker

When trying to build rust on Travis without using `stamp` or `docker`, both `RUSTC_COLOR=1` and `TRAVIS=true` will separately pass `--color always` to the command line. This causes the build to fail due to "*Option 'color' given more than once*".

In this PR, the `RUSTC_COLOR=1` will not be passed in the CI environment.

graydon/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust