fix: migrationsDir should accept relative path [#9]

Author: Tom Kirkpatrick

lib/models/migration.js

@@ -116,7 +116,8 @@ module.exports = function(Migration, options) {
             // include the script, run the up/down function, update the migrations table, and continue
             migrationStartTime = process.hrtime();
             Migration.log.info(localScriptName, 'running.');
-            require(path.join(Migration.migrationsDir, localScriptName))[upOrDown](Migration.app, function(err) {
+            const scriptPath = path.resolve(path.join(Migration.migrationsDir, localScriptName));
+            require(scriptPath)[upOrDown](Migration.app, function(err) {
               if (err) {
                 Migration.log.error(localScriptName, 'error:');
                 Migration.log.error(err.stack);