Try to add Ruby 3.0.0 support

[johannesluedke]

Issue: https://github.com/influxdata/influxdb-ruby/issues/245

From the warnings that pop up when running it with Ruby 2.7, I think those two methods need to be fixed:

• lib/influxdb/client.rb:52 (initialize), f.e. from spec/influxdb/cases/querying_issue_7000_spec.rb:9, spec/influxdb/cases/query_series_spec.rb:6
• lib/influxdb/query/core.rb:88 (query_params), f.e. from lib/influxdb/query/batch.rb:86

Without knowing the codebase it's not clear to me how to fix it.