Run migrations failed

[crocodile-bit]

Run migrations on node versions 10.19.0 and 12.16.3 failed with following error message. I created a pull request to fix this: #108

[ERROR] AssertionError [ERR_ASSERTION]: ifError got unwanted exception: dbm is not defined
    at /TechRadar/node_modules/db-migrate/lib/commands/on-complete.js:15:14
    at tryCatcher (/TechRadar/node_modules/bluebird/js/release/util.js:16:23)
    at Promise.successAdapter (/TechRadar/node_modules/bluebird/js/release/nodeify.js:22:30)
    at Promise._settlePromise (/TechRadar/node_modules/bluebird/js/release/promise.js:601:21)
    at Promise._settlePromiseCtx (/TechRadar/node_modules/bluebird/js/release/promise.js:641:10)
    at _drainQueueStep (/TechRadar/node_modules/bluebird/js/release/async.js:97:12)
    at _drainQueue (/TechRadar/node_modules/bluebird/js/release/async.js:86:9)
    at Async._drainQueues (/TechRadar/node_modules/bluebird/js/release/async.js:102:5)
    at Immediate.Async.drainQueues [as _onImmediate] (/TechRadar/node_modules/bluebird/js/release/async.js:15:14)
    at Object.<anonymous> (/TechRadar/migrations/20160525082319-create-db.js:1:1)
    at Module._compile (internal/modules/cjs/loader.js:1133:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1153:10)
    at Module.load (internal/modules/cjs/loader.js:977:32)
    at Function.Module._load (internal/modules/cjs/loader.js:877:14)
    at Module.require (internal/modules/cjs/loader.js:1019:19)
    at require (internal/modules/cjs/helpers.js:77:18)
    at Class.setup (/TechRadar/node_modules/db-migrate/lib/skeleton.js:158:12)
    at /TechRadar/node_modules/db-migrate/lib/migrator.js:231:41
From previous event:
    at /TechRadar/node_modules/db-migrate/lib/migrator.js:230:18
From previous event:
    at /TechRadar/node_modules/db-migrate/lib/migrator.js:225:14
    at /TechRadar/node_modules/db-migrate/lib/migration.js:368:7
    at processImmediate (internal/timers.js:456:21)