Fix docs indentation in pgtrgm.sgml
Fix docs indentation in pgtrgm.sgml

5871b884 introduced pg_trgm.word_similarity_threshold GUC, but its documentation
contains wrong indentation.  This commit fixes that.  Backpatch for easier
backpatching of other documentation fixes.

Discussion: https://postgr.es/m/4c735d30-ab59-fc0e-45d8-f90eb5ed3855%402ndquadrant.com
Author: Ian Barwick
Backpatch-through: 9.6

adam8157/gpdb,xinzweb/gpdb,xinzweb/gpdb,50wu/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,xinzweb/gpdb,adam8157/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb