tell JuliaInterface to load GAPDoc (#1009)

When `ENV["GAP_BARE_DEPS"]` is bound before GAP.jl gets loaded,
the JuliaInterface package will be loaded before GAPDoc,
and this causes a warning because JuliaInterface needs a
variable from GAPDoc.
In order to avoid this, add GAPDoc to the dependencies of
JuliaInterface.

pkg/JuliaInterface/PackageInfo.g

@@ -101,6 +101,7 @@ Dependencies := rec(
   GAP := ">= 4.11",    # need compatible code in GAP's src/julia_gc.c
   NeededOtherPackages := [ ],
   SuggestedOtherPackages := [ ],
+  OtherPackagesLoadedInAdvance := [ [ "GAPDoc", "1.6.6" ] ], # need StripEscapeSequences
   ExternalConditions := [ ],
 ),