Get appimagetool source from 'continuous' branch

Author: andy5995

Dockerfile

@@ -107,10 +107,8 @@ RUN \
 
 ARG CODENAME
 RUN \
-  git clone --depth 1 --branch main https://github.com/AppImage/appimagetool.git && \
+  git clone --depth 1 --branch continuous https://github.com/AppImage/appimagetool.git && \
   cd appimagetool && \
-  git fetch --depth 1 origin feac85722a75471fe62a3fbb5fe54dbccbc83729 && \
-  git checkout feac85722a75471fe62a3fbb5fe54dbccbc83729 && \
   cmake . -DCMAKE_INSTALL_PREFIX=$HOME/.local && \
   make install && \
   sudo apt install -y libzstd-dev && \