include header files in the tarball

haskell-igraph.cabal

@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                haskell-igraph
-version:             0.2.0
+version:             0.2.1
 synopsis:            Imcomplete igraph bindings
 description:         This is an attempt to create a complete bindings for the
                      igraph<"http://igraph.org/c/"> library. Related work:
@@ -15,6 +15,7 @@ copyright:           (c) 2016 Kai Zhang
 category:            Math
 build-type:          Simple
 cabal-version:       >=1.24
+extra-source-files:  cbits/haskelligraph.h
 
 Flag graphics
   Description: Enable graphics output
@@ -70,7 +71,6 @@ library
   default-language:    Haskell2010
   build-tools:         c2hs >=0.25.0
   c-sources:           cbits/haskelligraph.c
-  include-dirs:        cbits
   includes:            cbits/haskelligraph.h
 
 test-suite tests