Added support for timestamp-based migrations

Signed-off-by: Jonathon Hill <jhill@brandmovers.com>
diff --git a/system/language/english/migration_lang.php b/system/language/english/migration_lang.php
index 5753c00..a262d30 100644
--- a/system/language/english/migration_lang.php
+++ b/system/language/english/migration_lang.php
@@ -27,6 +27,7 @@
 
 $lang['migration_none_found']			= 'No migrations were found.';
 $lang['migration_not_found']			= 'No migration could be found with the version number: %d.';
+$lang['migration_sequence_gap']         = 'There is a gap in the migration sequence near version number: %d.';
 $lang['migration_multiple_version']		= 'There are multiple migrations with the same version number: %d.';
 $lang['migration_class_doesnt_exist']	= 'The migration class "%s" could not be found.';
 $lang['migration_missing_up_method']	= 'The migration class "%s" is missing an "up" method.';