fix(0.4/2015-06-22--image_url.xml): explicitly cast a string to an integer on PostgreSQL.

The failure was:
liquibase.exception.DatabaseException: ERROR: column "image_id" is of type integer but expression is of type text
Hint: You will need to rewrite or cast the expression.
Position: 75 [Failed SQL: INSERT INTO series_images(series_id, image_id) SELECT id AS series_id, REPLACE(image_url, '/image/', '') AS image_id FROM series]

Addressed to #1034

Author: php-coder

src/main/resources/liquibase/version/0.4/2015-06-22--image_url.xml

@@ -34,12 +34,19 @@
 
 		<comment>Migrates data from series.image_url to series_images</comment>
 
-		<sql>
+		<sql dbms="mysql,h2">
 			INSERT INTO series_images(series_id, image_id)
 			SELECT id AS series_id, REPLACE(image_url, '/image/', '') AS image_id
 			FROM series
 		</sql>
 
+		<!-- PostgreSQL requires us to cast a string to an integer explicitly -->
+		<sql dbms="postgresql">
+			INSERT INTO series_images(series_id, image_id)
+			SELECT id AS series_id, CAST(REPLACE(image_url, '/image/', '') AS INT) AS image_id
+			FROM series
+		</sql>
+		
 	</changeSet>
 
 	<changeSet id="drop-image_url-column-from-series-table" author="php-coder" context="scheme">