Travis: Run Chutney jobs in Ubuntu Bionic images

Closes 32240.

.travis.yml

@@ -41,10 +41,6 @@ matrix:
     ## Use -std=gnu99 to turn off some newer features, and maybe turn on some
     ## extra gcc warnings?
     - env: CHUTNEY="yes" CHUTNEY_ALLOW_FAILURES="2" SKIP_MAKE_CHECK="yes" C_DIALECT_OPTIONS="-std=gnu99"
-      ## (Linux only) Use an older Linux image (Ubuntu Trusty)
-      ## The Xenial and Bionic images cause permissions issues for chutney,
-      ## this is a workaround, until we fix #32240.
-      dist: trusty
     ## We check asciidoc with distcheck, to make sure we remove doc products
     ## We use Linux clang, because there are no other Linux clang jobs
     - env: DISTCHECK="yes" ASCIIDOC_OPTIONS="" SKIP_MAKE_CHECK="yes"