Fix pronto hooks with warning level

[Drowze]

Pronto might report warnings and that was not being correctly parsed by Overcommit. This is sort of a follow-up from #754.

Before: all warnings and errors were reported as errors. They actually simply crashed at

overcommit/lib/overcommit/utils/messages_utils.rb

Lines 23 to 30 in 7d94fa5

	def extract_messages(output_messages, regex, type_categorizer = nil)
	output_messages.map.with_index do |message, index|
	unless match = message.match(regex)
	raise Overcommit::Exceptions::MessageProcessingError,
	'Unexpected output: unable to determine line number or type ' \
	"of error/warning for output:\n" \
	"#{output_messages[index..-1].join("\n")}"
	end

Now warnings and errors are reported correctly. Examples below:

# Testing with an output containing only warnings
⋊> ~/w/o/cts on rg-test-branch ⨯ be pronto run --exit-code --commit=qa --runner reek
Running Pronto::Reek
app/models/shipment.rb:163 W: Calls 'loc.type' 3 times - [DuplicateMethodCall](https://github.com/troessner/reek/blob/v6.0.4/docs/Duplicate-Method-Call.md)

⋊> ~/w/o/cts on rg-test-branch ⨯ git push --dry-run origin HEAD # using a hook with reek
Running pre-push hooks
Analyzing with Pronto (brakeman, fasterer, flay and reek)[Pronto] WARNING
app/models/shipment.rb:163 W: Calls 'loc.type' 3 times - [DuplicateMethodCall](https://github.com/troessner/reek/blob/v6.0.4/docs/Duplicate-Method-Call.md)

⚠ All pre-push hooks passed, but with warnings

# Testing with an output containing warnings AND errors
⋊> ~/w/o/cts on rg-test-branch ⨯ be pronto run --exit-code --commit=qa --runner rubocop
Running Pronto::Rubocop
app/models/shipment.rb:158 E: Layout/MultilineOperationIndentation: Use 2 (not 3) spaces for indenting an expression spanning multiple lines.

 ``suggestion
          loc.status == Models::Location::STATUS_CURRENT
 ``

⋊> ~/w/o/cts on rg-test-branch ⨯ git push --dry-run origin HEAD # using a hook with reek and rubocop
Running pre-push hooks
Analyzing with Pronto (brakeman, fasterer, flay, reek and rubocop)[Pronto] FAILED
app/models/shipment.rb:163 W: Calls 'loc.type' 3 times - [DuplicateMethodCall](https://github.com/troessner/reek/blob/v6.0.4/docs/Duplicate-Method-Call.md)
app/models/shipment.rb:158 E: Layout/MultilineOperationIndentation: Use 2 (not 3) spaces for indenting an expression spanning multiple lines.

✗ One or more pre-push hooks failed

error: failed to push some refs to 'git@github.com:Org/cts'

[sds]

Thank you.