Upgraded appveyor dockerfile reference to zlib to 1.2.13
Patch: JensG
diff --git a/build/docker/msvc2017/Dockerfile b/build/docker/msvc2017/Dockerfile
index d59c195..a5c04b7 100644
--- a/build/docker/msvc2017/Dockerfile
+++ b/build/docker/msvc2017/Dockerfile
@@ -67,7 +67,7 @@
# Install zlib
COPY appveyor\build-zlib.bat C:\TEMP\build-zlib.bat
-ENV ZLIB_VERSION=1.2.11
+ENV ZLIB_VERSION=1.2.13
ENV WIN3P=C:\TEMP\WIN3P
RUN C:\BuildTools\Common7\Tools\VsDevCmd.bat -arch=amd64 && `
MKDIR C:\TEMP\WIN3P && `