Updated to latest client API, fixed float regexp, skipping empty cells

[smamessier]

Made a couple of changes to make it work (better)

• Newest InfluxDB client repository changed from /influxdb to /influxdata
• Newest InfluxDB client API renames Client to HTTPClient
• Existing float REGEXP didn't cover negative floats or scientific floats
• Added if clause to skip empty cells (Empty cells were inserted as string and therefore, any additional entry of non-string type would generate a type conflict error)

[jpillora]

Thanks!