arabic: add api to -path flags in AllAra.gf and LangAra.gf

This fixes a build problem (either a type error, if doing an incremental
rebuild, or a failure to find SyntaxAra.gf if building from scratch.)
I wonder why the Travis build didn't catch this?

src/arabic/AllAra.gf

@@ -1,3 +1,3 @@
---# -path=.:../abstract:../common:../prelude
+--# -path=.:../abstract:../common:../api:../prelude
 
 concrete AllAra of AllAraAbs = LangAra ;

src/arabic/LangAra.gf

@@ -1,4 +1,4 @@
---# -path=.:../abstract:../common:../prelude
+--# -path=.:../abstract:../common:../api:../prelude
 
 concrete LangAra of Lang = 
   GrammarAra,