install: install `giflib`

install

@@ -5,6 +5,7 @@ PIXMAN="http://www.cairographics.org/releases/pixman-0.32.4.tar.gz"
 CAIRO="http://cairographics.org/releases/cairo-1.12.16.tar.xz"
 FREETYPE="http://download.savannah.gnu.org/releases/freetype/freetype-2.4.10.tar.gz"
 LIBPNG="http://downloads.sourceforge.net/project/libpng/libpng16/1.6.10/libpng-1.6.10.tar.gz"
+GIF_LIB="http://downloads.sourceforge.net/project/giflib/giflib-5.1.0.tar.gz"
 PREFIX=${1-/usr/local}
 
 require() {
@@ -58,6 +59,7 @@ require tar
 test `which pkg-config` || fetch $PKG_CONFIG
 require 'pkg-config'
 fetch $LIBPNG
+fetch $GIF_LIB
 fetch $FREETYPE
 fetch $PIXMAN
 fetch_xz $CAIRO