feat: then-fs -> promise-fs

then-fs seems to be causing a memory leak in jest in other tools.

Found by jestjs/jest#8331

lib/index.js

@@ -1,7 +1,7 @@
 module.exports = resolvePkg;
 module.exports.sync = sync;
 
-var fs = require('then-fs');
+var fs = require('promise-fs');
 var path = require('path');
 var debug = require('debug')('snyk:resolve');
 

package.json

@@ -16,7 +16,7 @@
   "license": "Apache-2.0",
   "dependencies": {
     "debug": "^4.1.1",
-    "then-fs": "^2.0.0"
+    "promise-fs": "^2.1.1"
   },
   "devDependencies": {
     "es6-promise": "^4.2.8",

test/index.test.js

@@ -31,7 +31,7 @@ var fs = {
 };
 
 var resolve = proxyquire('../lib/index', {
-  'then-fs': fs,
+  'promise-fs': fs,
 });
 
 test('resolve immediately', function (t) {
@@ -140,4 +140,4 @@ test('resolve works with scoped packages', function (t) {
   });
 
   t.equal(resolve.sync('@remy/foo', base), path.dirname(target), 'sync scoped matches');
-});
+});