fix oracle interval type

Author: jogibear9988

src/Migrator/Providers/Impl/Oracle/OracleDialect.cs

@@ -45,7 +45,7 @@ public OracleDialect()
 			RegisterColumnType(DbType.String, int.MaxValue, "NCLOB");
 			RegisterColumnType(DbType.Time, "DATE");
 			RegisterColumnType(DbType.Guid, "RAW(16)");
-			RegisterColumnType(MigratorDbType.Interval, "NUMBER(20,0)");
+			RegisterColumnType(MigratorDbType.Interval, "interval day (9) to second (9)");
 
 			// the original Migrator.Net code had this, but it's a bad idea - when
 			// apply a "null" migration to a "not-null" field, it just leaves it as "not-null" and silent fails