User agent specific GWT modules are used for development only. The build
is triggered from the IDE (Eclipse) in GWT compile filter.
It turns out, that ie11 and edge are not valid user agents, but known as
gecko1_8. Change it in Buck code as well.
TEST PLAN:
$ bazel build gerrit-gwtui/...
Contributed-By: Damien Martin-Guillerez <dmarting@google.com>
Change-Id: I0c8731f765fda2824bb5145abdb12e295658fe04