docs: update Line Protocol doc url from 1.6 to latest (#129)

Author: timbeccue

README.rst

@@ -46,7 +46,7 @@ InfluxDB 2.0 client features
     - into csv, raw data, `flux_table <https://github.com/influxdata/influxdb-client-python/blob/master/influxdb_client/client/flux_table.py#L5>`_ structure, `Pandas DataFrame <https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.html>`_
     - `How to queries <#queries>`_
 - Writing data using
-    - `Line Protocol <https://docs.influxdata.com/influxdb/v1.6/write_protocols/line_protocol_tutorial>`_
+    - `Line Protocol <https://docs.influxdata.com/influxdb/latest/write_protocols/line_protocol_tutorial>`_
     - `Data Point <https://github.com/influxdata/influxdb-client-python/blob/master/influxdb_client/client/write/point.py#L16>`__
     - `RxPY <https://rxpy.readthedocs.io/en/latest/>`__ Observable
     - `Pandas DataFrame <https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.html>`_
@@ -208,7 +208,7 @@ Writes
 .. marker-writes-start
 
 The `WriteApi <https://github.com/influxdata/influxdb-client-python/blob/master/influxdb_client/client/write_api.py>`_ supports synchronous, asynchronous and batching writes into InfluxDB 2.0.
-The data should be passed as a `InfluxDB Line Protocol <https://docs.influxdata.com/influxdb/v1.6/write_protocols/line_protocol_tutorial/>`_\ , `Data Point <https://github.com/influxdata/influxdb-client-python/blob/master/influxdb_client/client/write/point.py>`_ or Observable stream.
+The data should be passed as a `InfluxDB Line Protocol <https://docs.influxdata.com/influxdb/latest/write_protocols/line_protocol_tutorial/>`_\ , `Data Point <https://github.com/influxdata/influxdb-client-python/blob/master/influxdb_client/client/write/point.py>`_ or Observable stream.
 
 *The default instance of WriteApi use batching.*