Use Charset name instead of relying on toString()
Use Charset name instead of relying on toString()

Use the `Charset.name()` method to get the charset code instead of
relying on the `toString()` method of the Charset implementation. It
seems that on Android the `toString()` method does not always return the
charset code as expected.

Fixes #272.

fernandopeinado/influxdb-java,fernandopeinado/influxdb-java,influxdb/influxdb-java,influxdata/influxdb-java,influxdata/influxdb-java