Update fielddata.asciidoc

Fixed default value for circuit breaker

docs/reference/index-modules/fielddata.asciidoc

@@ -37,7 +37,7 @@ parameters:
 |=======================================================================
 |Setting |Description
 |`indices.fielddata.breaker.limit` |Maximum size of estimated field data
-to allow loading. Defaults to 80% of the maximum JVM heap.
+to allow loading. Defaults to 60% of the maximum JVM heap.
 |`indices.fielddata.breaker.overhead` |A constant that all field data
 estimations are multiplied with to determine a final estimation. Defaults to
 1.03