Changed epoch parameter to be in compliance with documentation.

See current documentation https://docs.influxdata.com/influxdb/v1.7/guides/querying_data/#other-options-when-querying-data

This is also present in old documentation, at least since version 0.13 https://docs.influxdata.com/influxdb/v0.13/guides/querying_data/#other-options-when-querying-data

Author: fredo994

src/main/java/org/influxdb/impl/TimeUtil.java

@@ -60,7 +60,7 @@ public static String toTimePrecision(final TimeUnit t) {
     case MICROSECONDS:
       return "u";
     case NANOSECONDS:
-      return "n";
+      return "ns";
     default:
       throw new IllegalArgumentException("time precision must be one of:" + ALLOWED_TIMEUNITS);
     }