Update env-var in Dockerfile, fix volume names

docker-compose.yml.example

@@ -8,8 +8,8 @@ services:
             # modifying the part before the `:`.
             - "8000:8000"
         volumes:
-            - paperless-data:/usr/src/paperless/data
-            - paperless-media:/usr/src/paperless/media
+            - data:/usr/src/paperless/data
+            - media:/usr/src/paperless/media
         env_file: docker-compose.env
         environment:
             - PAPERLESS_OCR_LANGUAGES=
@@ -18,20 +18,20 @@ services:
     consumer:
         image: paperless
         volumes:
-            - paperless-data:/usr/src/paperless/data
-            - paperless-media:/usr/src/paperless/media
+            - data:/usr/src/paperless/data
+            - media:/usr/src/paperless/media
             # You have to adapt the local path you want the consumption
             # directory to mount to by modifying the part before the ':'.
             - /path/to/arbitrary/place:/consume
             # Likewise, you can add a local path to mount a directory for
             # exporting. This is not strictly needed for paperless to
             # function, only if you're exporting your files: uncomment
-            # it and fill in a local path if you know you're going to 
+            # it and fill in a local path if you know you're going to
             # want to export your documents.
             # - /path/to/another/arbitrary/place:/export
         env_file: docker-compose.env
         command: ["document_consumer"]
 
 volumes:
-    paperless-data:
-    paperless-media:
+    data:
+    media: