Attempt to reduce size a bit more

- Ignore the cruft when building
 - Remove the correct temporary directory

#32 - Docker image

.dockerignore

@@ -0,0 +1,4 @@
+.gradle/
+.idea/
+.git/
+Dockerfile

Dockerfile

@@ -5,12 +5,13 @@ ARG DOCKER_IMAGE_VERSION=unknown
 
 # JDK version
 ARG JDK=9
-ARG TMP_DIR=muwire-tmp
 
+# Important directories
+ARG TMP_DIR=/muwire-tmp
 ENV APP_HOME=/muwire
 
 # Define working directory.
-WORKDIR /$TMP_DIR
+WORKDIR $TMP_DIR
 
 # Put sources into dir
 COPY . .