Update vcpkg

(MXNet 1.3.0)

windows/Dockerfile

@@ -56,7 +56,7 @@ RUN [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tl
 RUN $vcpkg_dir = 'C:/vcpkg'; \
     git clone --depth=1 https://github.com/BioroboticsLab/RF_vcpkg.git $vcpkg_dir; \
     cd $vcpkg_dir; \
-    git checkout 247c77cbdee32767707f0390e1b4b4d16c2a9fef; \
+    git checkout c40c60c32efff9a953e9c560f63a80ee0ab4a5d9; \
     ./scripts/bootstrap.ps1; \
     [Environment]::SetEnvironmentVariable('VCPKG_DIR', "\"$vcpkg_dir\"", [EnvironmentVariableTarget]::Machine);