Update the documentation to generalize the PATH location

The documentation was generated from the ruby code on my machine, which
mean the default value was reflected the location on my laptop.

Fixes #297

Author: ph

docs/index.asciidoc

@@ -366,7 +366,7 @@ How often to validate a connection (in seconds)
 ===== `last_run_metadata_path`
 
   * Value type is <<string,string>>
-  * Default value is `"/home/ph/.logstash_jdbc_last_run"`
+  * Default value is `"$HOME/.logstash_jdbc_last_run"`
 
 Path to file with last run time
 
@@ -487,4 +487,4 @@ to `false`, `:sql_last_value` reflects the last time the query was executed.
 [id="plugins-{type}s-{plugin}-common-options"]
 include::{include_path}/{type}.asciidoc[]
 
-:default_codec!:
+:default_codec!: