[fix] docker 'Error compiling' and 'SyntaxError' messages

The make docker target spits out some SyntaxError.  With this .dockerignore
there is no more error. Explanation:

- the python files are compiled while building the docker image
- a node modules contains some python files
- the python files inside the node module doesn't compile

It raises the fact that node_modules were included in the docker image which
should not happen.  Same the local directory was included.  Dockerfile builds
searx in its own way (without virtualenv)

Thanks @dalf:

- https://github.com/asciimoo/searx/pull/1900#issuecomment-604892737



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>