Update configuration.md

Change `ssl` option example for postgres from `string` like value to `boolean` to prevent misleading.

Author: minhnhut

docs/Getting Started/configuration.md

@@ -27,7 +27,7 @@ db-migrate supports the concept of environments. For example, you might have a d
     "host": "localhost",
     "database": "mydb",
     "port": "20144",
-    "ssl": "true",
+    "ssl": true,
     "schema": "my_schema"
   },