Update /dashboard location in nginux

[parberge]

Description

Change the nginx config to partly solve #353.
/dashboard will now redirect to the selenium hub page instead.
/dashboard/ will show the zalenium dashboard.

Motivation and Context

People got redirected to a 404 page when the port mapping wasn't 4444:4444.

How Has This Been Tested?

mvn clean package -DskipTests=true -Pbuild-docker-image

$ docker run --rm -ti --name zalenium -p 80:4444 \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -v /tmp/videos:/home/seluser/videos \
--privileged zalenium:3.10.0c-SNAPSHOT start

curl localhost/dashboard <-- result in selenium hub page
curl localhost/dashboard/ <-- result in zalenium dashboard

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have read the CONTRIBUTING document.

[codecov-io]

Codecov Report

Merging #474 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #474      +/-   ##
============================================
- Coverage     78.66%   78.62%   -0.04%     
- Complexity      556      557       +1     
============================================
  Files            31       31              
  Lines          2601     2601              
  Branches        225      225              
============================================
- Hits           2046     2045       -1     
- Misses          420      424       +4     
+ Partials        135      132       -3

[diemol]

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[parberge]

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