Use \/ to avoid en-dash ligature instead of -{}-.

This is to fix LuaLaTeX output. The -{}- sequence does not avoid the
ligature with LuaLaTeX but \/ does.
Merge remote-tracking branch 'origin/master' into en-dash-ligature-avoidance.
Merge pull request #1145 from wilx/en-dash-ligature-avoidance

Use \/ to avoid en-dash ligature instead of -{}-.