Fix dependencies.

Author: davidgiven

.github/workflows/ccpp.yml

@@ -65,7 +65,7 @@ jobs:
         path: 'fluxengine-testdata'
     - name: brew
       run: |
-        brew install sqlite pkg-config libusb protobuf wxwidgets fmt make coreutils dylibbundler libjpeg libmagic nlohmann-json cli11 boost glfw3
+        brew install sqlite pkg-config libusb protobuf wxwidgets fmt make coreutils dylibbundler libjpeg libmagic nlohmann-json cli11 boost glfw3 md4c
     - name: make
       run: gmake -C fluxengine
     - name: Upload build artifacts