Merge pull request python-pillow#56 from radarhere/zlib

Update zlib to 1.2.11

Author: hugovk

archives/zlib-1.2.11.tar.xz

@@ -4,7 +4,7 @@
 # Package versions for fresh source builds
 FREETYPE_VERSION=2.7.1
 LIBPNG_VERSION=1.6.25
-ZLIB_VERSION=1.2.10
+ZLIB_VERSION=1.2.11
 JPEG_VERSION=9b
 OPENJPEG_VERSION=2.1
 TIFF_VERSION=4.0.7