Revert "travis: Switch to autobuilt Docker images"

This reverts commit b2e52408f7.
Turns out only [testing] is on PyQt 5.6, and even with that the testsuite
doesn't seem to load properly...

scripts/dev/ci/travis_run.sh

@@ -1,8 +1,12 @@
 #!/bin/bash
 
 if [[ $DOCKER ]]; then
+    # To build a fresh image:
+    # docker build -t img misc/docker/$DOCKER
+    # docker run --privileged -v $PWD:/outside img
+
     docker run --privileged -v $PWD:/outside \
-        thecompiler/qutebrowser:$DOCKER
+        thecompiler/qutebrowser-manual:$DOCKER
 else
     args=()
     [[ $TESTENV == docs ]] && args=('--no-authors')