Fix typo. Make the environment variable MONGODB_URL not MONGODB_URI

[bramblek1]

Despite the flag being called mongodb.uri, the documentation and the default
value of mongdb.uri refer to the env var MONGODB_URL

When overriding this prior to creating a test connection , the value of os.GetEnv("MONGODB_URI") is used to override.

In the scenario where you've got mongodb_exporter being launched with a flag for the mongdb.uri AND you're overriding that with MONGODB_URL in the environment. Results are confusing.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #113 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master     #113   +/-   ##
=======================================
  Coverage   28.92%   28.92%           
=======================================
  Files          42       42           
  Lines        2254     2254           
=======================================
  Hits          652      652           
  Misses       1564     1564           
  Partials       38       38

Impacted Files	Coverage Δ
mongodb_exporter.go	3.5% <0%> (ø)	⬆️

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[arvenil]

Hi @bramblek1
Thank you for your contribution. This sadly goes on hold. The problem is this exporter is part of PMM and PMM uses MONGODB_URI instead. Looks like old error we need to fix but it will need to wait until we fix it also in PMM, which may take some time as we need to keep also backward compatibility. In the meantime you can use MONGODB_URI instead. I've also filled upstream bug report to clarify this dcu/mongodb_exporter#108.

[AlekSi]

We will use URI instead of URL everywhere.