travis: Wait at most 30 minutes for base test

Sometimes travis gets slow and makes the builds spurious failure because
of no output in 10 minutes. This commit increase Travis timing-out time
at most 30 minutes before terminating the build.

Author: tesuji

.travis.yml

@@ -98,7 +98,7 @@ script:
       export LD_LIBRARY_PATH=$(rustc --print sysroot)/lib
   - |
     if [ -z ${INTEGRATION} ]; then
-      ./ci/base-tests.sh && sleep 5
+      travis_wait 30 ./ci/base-tests.sh && sleep 5
     else
       ./ci/integration-tests.sh && sleep 5
     fi