Fix #133 - support influxdb v1.8 HTTP error response message

An influxdb v1.8 HTTP error response message was not correctly transfered to ruby InfluxError message.
In case of an InfuxError, the reason (except status code) was not traceable.

How the fix works:
- InfluxDB v1.8 and v2.x provide Error details in the json-rsp body
- InfluxDB v2.x uses the `message` key for this
- InfluxDB v1.8 uses the `error` key for this

-> previously only `message` was supported
-> now, in case `message` is empty, `error` is checked

lib/influxdb2/client/influx_error.rb

@@ -32,7 +32,7 @@ def initialize(original = nil, message:, code:, reference:, retry_after:)
 
     def self.from_response(response)
       json = JSON.parse(response.body)
-      obj = new(message: json['message'] || '', code: response.code, reference: json['code'] || '',
+      obj = new(message: json['message'] || json['error'] || '', code: response.code, reference: json['code'] || '',
                 retry_after: response['Retry-After'] || '')
       obj
     rescue JSON::ParserError