aspell: disable parrallel build

Sometimes we observe:

    /usr/bin/ld: cannot find -laspell
    collect2: error: ld returned 1 exit status
    libtool: install: error: relink `email-filter.la' with the above command before installing it
    Makefile:960: recipe for target 'install-filterLTLIBRARIES' failed

/reviewed-on !652

component/aspell/buildout.cfg

@@ -22,6 +22,8 @@ environment =
   PATH=${patch:location}/bin:${perl:location}/bin:%(PATH)s
   CPPFLAGS=-I${ncurses:location}/include
   LDFLAGS=-L${ncurses:location}/lib -Wl,-rpath=${ncurses:location}/lib
+# aspell parallel build sometimes fail
+make-options = -j1
 
 [aspell-en-dictionary]
 <= aspell-dictionary-common