Fix ledger file in examples folder (#447)

The example file for creating unique index was merged,
but the file name was not correct. Now the filename,
the ledger and the readme link is fixed.

Author: kvch

docs/README.md

@@ -981,7 +981,7 @@ Example **create index** migrations:
 * [10_create_index.json](../examples/10_create_index.json)
 * [37_create_partial_index.json](../examples/37_create_partial_index.json)
 * [38_create_hash_index_with_fillfactor.json](../examples/38_create_hash_index_with_fillfactor.json)
-* [39_create_unique_index.json](../examples/39_create_unique_index.json)
+* [42_create_unique_index.json](../examples/42_create_unique_index.json)
 
 ### Create table
 

examples/.ledger

@@ -39,3 +39,4 @@
 39_add_column_with_multiple_pk_in_table.json
 40_create_enum_type.json
 41_add_enum_column.json
+42_create_unique_index.json

examples/39_create_unique_index.json renamed to examples/42_create_unique_index.json

@@ -1,5 +1,5 @@
 {
-  "name": "39_create_unique_index",
+  "name": "42_create_unique_index",
   "operations": [
     {
       "create_index": {