Ignore filenames starting with '.' but not the current dir

In the Hyperledger Fabric docker agent, I want to igore files starting
with '.' like `.venv` for the python virtual environment for personal
development. Thus, I added `.*` in the `.dockerignore`. However,
this causes a warning when building the docker image because for
`COPY . .` because the current path `.` is also included in `.*`.
Therefore, `!.` is added to the dockerfile to suppress the warning.

Signed-off-by: dodo920306 <dodo920306@gmail.com>

Author: dodo920306

src/agents/hyperledger-fabric/.dockerignore

@@ -1,3 +1,4 @@
 .*
+!.
 cello
 hyperledger_cello_hyperledger_fabric_agent