Fix the accelerators for next/previous in RTL

Fixes: GNOME/epiphany#239
3 jobs from fix-nav-rtl in 16 minutes and 45 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #185970
flatpak

00:15:37

 
  Deploy
passed #185971
review

00:00:35

failed #185972
allowed to fail manual
stop_review

00:00:32

 
Name Stage Failure
failed
stop_review Deploy
Using Docker executor with image fedora:29 ...
Pulling docker image fedora:29 ...
Using docker image sha256:8bd04269a51be87e39303d97c8f645a39016fcc2bd235e41812e0cfb96b283e3 for fedora:29 ...
Running on runner-d836cf30-project-3369-concurrent-1 via gcc150.bak.milne.osuosl.org...
Cloning repository...
Cloning into '/builds/jbrummer/epiphany'...
Checking out 0cabbc17 as fix-nav-rtl...
fatal: reference is not a tree: 0cabbc178270865a801d1f7d3c9f127654dc11e0
ERROR: Job failed: exit code 1