Added PostgreSQL REAL data type (#18513)

* Added PostgreSQL REAL data type

Adds support for PostgresSQL's REAL data type.

That way you can have real columns in your schema:

```php
$table->addColumn('real', $column)
```

* Update PostgresGrammar.php

src/Illuminate/Database/Schema/Grammars/PostgresGrammar.php

@@ -385,6 +385,17 @@ protected function typeDouble(Fluent $column)
         return 'double precision';
     }
 
+    /**
+     * Create the column definition for a real type.
+     *
+     * @param  \Illuminate\Support\Fluent  $column
+     * @return string
+     */
+    protected function typeReal(Fluent $column)
+    {
+        return 'real';
+    }
+
     /**
      * Create the column definition for a decimal type.
      *