move image file

Author: abarbu

matplotlib.cabal

@@ -10,7 +10,7 @@ maintainer: andrei@0xab.com
 copyright: 2017 Andrei Barbu
 category: Graphics
 build-type: Simple
-extra-source-files: README.md contour.png
+extra-source-files: README.md imgs/contour.png
 cabal-version: >=1.10
 
 library