Fix version number in pc file after PROJECTS change.

Fixes #177
diff --git a/libzip.pc.in b/libzip.pc.in
index c2565a8..58b3dca 100644
--- a/libzip.pc.in
+++ b/libzip.pc.in
@@ -8,7 +8,7 @@
 
 Name: libzip
 Description: library for handling zip archives
-Version: @VERSION@
+Version: @PROJECT_VERSION@
 Libs: @PKG_CONFIG_RPATH@ -L${libdir} -lzip
 Libs.private: @LIBS@
 Cflags: -I${includedir}