Make cargo new independent of workdir to be exact

The muslrust images seem to have a workdir of /volume as opposed to / in the
others so doing cargo new like this would create the folder in /volume/app.

docker/armv7/sqlite/Dockerfile

@@ -48,7 +48,7 @@ RUN sed 's/^deb/deb-src/' /etc/apt/sources.list > \
         libc6-dev:armhf
 
 # Creates a dummy project used to grab dependencies
-RUN USER=root cargo new --bin app
+RUN USER=root cargo new --bin /app
 WORKDIR /app
 
 # Copies over *only* your manifests and build files