Travis build timeout

[tesuji]

Build timeout for dogfood and dogfood_tests:

test dogfood_tests ... test dogfood_tests has been running for over 60 seconds
test dogfood ... test dogfood has been running for over 60 seconds
No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received
The build has been terminated

Happened in:

• https://travis-ci.com/rust-lang/rust-clippy/jobs/204692251#L1307
• https://travis-ci.com/rust-lang/rust-clippy/jobs/204682946#L1307
• https://travis-ci.com/rust-lang/rust-clippy/jobs/204695123#L1307

[tesuji]

Fixed by #4200