webp: add hash for license file

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/webp/webp.hash

@@ -1,2 +1,3 @@
 # Locally calculated
 sha256	c928119229d4f8f35e20113ffb61f281eda267634a8dc2285af4b0ee27cf2b40	libwebp-0.6.0.tar.gz
+sha256	5aec868f669e384a22372a4e8a1a6cd7d44c64cd451f960ca69cc170d1e13acf	COPYING