make run leads to 'invalid mount config for type "bind"' error

[dasmur]

Unfortunately, my pull request #65 introduced an error into the Makefiles run target, resulting in the following error:

sudo docker run -it --mount type=bind,src="",destination=/landkreise crawler
docker: Error response from daemon: invalid mount config for type "bind": field Source must not be empty.
See 'docker run --help'.
Makefile:4: recipe for target 'run' failed
make: *** [run] Error 125

Root cause
The current run target uses $(pwd) in the middle of the command which should spawn a subshell, but instead make itself expands this to a variable (which does not exist), resulting in an empty value for src=.

Solution
Escape the $ by using $$.