Update zlib URL (#7474)

* Update zlib URL

Per #7468

* Update Dockerfile

Author: oliverchang

projects/libspng/Dockerfile

@@ -23,9 +23,9 @@ RUN apt-get update && \
 RUN git clone --depth 1 https://github.com/randy408/libspng.git
 RUN git clone --depth 1 https://github.com/google/fuzzer-test-suite
 
-RUN wget -O $WORK/zlib.tar.gz http://www.zlib.net/zlib-1.2.11.tar.gz
+RUN wget -O $WORK/zlib.tar.gz http://www.zlib.net/zlib-1.2.12.tar.gz
 RUN tar xzvf $WORK/zlib.tar.gz --directory $SRC/
-RUN mv $SRC/zlib-1.2.11 $SRC/zlib
+RUN mv $SRC/zlib-1.2.12 $SRC/zlib
 
 WORKDIR libspng
 COPY build.sh $SRC/