feat(ignored files): warn about ignored files in migrations directory

@yannvr pointed out in #108 that if there is some extra files in migrations
directory, it might be a sign of invalid pattern. In the most common use case,
there is only migrations in migrations directory. => If there is other files,
the pattern is probably filtering out some migrations.

src/index.js

@@ -416,7 +416,11 @@ module.exports = redefine.Class(/** @lends Umzug.prototype */ {
       .promisify(fs.readdir)(this.options.migrations.path)
       .bind(this)
       .filter(function (file) {
-        return this.options.migrations.pattern.test(file);
+        if(!this.options.migrations.pattern.test(file)) {
+          this.log('File: ' + file + ' does not match pattern: ' + this.options.migrations.pattern);
+          return false;
+        }
+        return true;
       })
       .map(function (file) {
         return path.resolve(this.options.migrations.path, file);

test/index/execute.test.js

@@ -45,9 +45,10 @@ describe('execute', function () {
       .then(function () {
         expect(this.upStub.callCount).to.equal(1);
         expect(this.downStub.callCount).to.equal(0);
-        expect(this.logSpy.callCount).to.equal(2);
-        expect(this.logSpy.getCall(0).args[0]).to.equal('== 123-migration: migrating =======');
-        expect(this.logSpy.getCall(1).args[0]).to.match(/== 123-migration: migrated \(0\.0\d\ds\)/);
+        expect(this.logSpy.callCount).to.equal(3);
+        expect(this.logSpy.getCall(0).args[0]).to.match(/File: \.gitkeep does not match pattern: .+/);
+        expect(this.logSpy.getCall(1).args[0]).to.equal('== 123-migration: migrating =======');
+        expect(this.logSpy.getCall(2).args[0]).to.match(/== 123-migration: migrated \(0\.0\d\ds\)/);
         expect(this.migratingEventSpy.calledWith('123-migration')).to.equal(true);
         expect(this.migratedEventSpy.calledWith('123-migration')).to.equal(true);
       });
@@ -59,9 +60,10 @@ describe('execute', function () {
       .then(function () {
         expect(this.upStub.callCount).to.equal(0);
         expect(this.downStub.callCount).to.equal(1);
-        expect(this.logSpy.callCount).to.equal(2);
-        expect(this.logSpy.getCall(0).args[0]).to.equal('== 123-migration: reverting =======');
-        expect(this.logSpy.getCall(1).args[0]).to.match(/== 123-migration: reverted \(0\.0\d\ds\)/);
+        expect(this.logSpy.callCount).to.equal(3);
+        expect(this.logSpy.getCall(0).args[0]).to.match(/File: \.gitkeep does not match pattern: .+/);
+        expect(this.logSpy.getCall(1).args[0]).to.equal('== 123-migration: reverting =======');
+        expect(this.logSpy.getCall(2).args[0]).to.match(/== 123-migration: reverted \(0\.0\d\ds\)/);
         expect(this.revertingEventSpy.calledWith('123-migration')).to.equal(true);
         expect(this.revertedEventSpy.calledWith('123-migration')).to.equal(true);
       });