RangePicker with format is not working

### Issue type

**I'm submitting a ...** (check one with "x")

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**

When i set a format to rangepicker and pick a range nothing shows in the input

**Expected behavior:**

the dates need to show up

**Steps to reproduce:**

**Related code:**

```

```

### Other information:

**npm, node, OS, Browser**
```

node -v
v12.18.3

npm -v
6.14.6

OS: Windows 10
Browser: Chrome

```

**Angular, Nebular**
```
"dependencies": {
"@angular/animations": "~11.2.7",
"@angular/cdk": "^10.2.1",
"@angular/common": "~11.2.7",
"@angular/compiler": "~11.2.7",
"@angular/core": "~11.2.7",
"@angular/forms": "~11.2.7",
"@angular/platform-browser": "~11.2.7",
"@angular/platform-browser-dynamic": "~11.2.7",
"@angular/router": "~11.2.7",
"@angular/service-worker": "^11.2.7",
"@fortawesome/fontawesome-svg-core": "^1.2.28",
"@fortawesome/free-brands-svg-icons": "^5.13.0",
"@fortawesome/free-regular-svg-icons": "^5.13.0",
"@nebular/eva-icons": "6.2.1",
"@nebular/theme": "^6.2.1",
"@ngx-translate/core": "^13.0.0",
"@ngx-translate/http-loader": "^6.0.0",
"angular2-signaturepad": "^2.11.0",
"bootstrap": "^4.5.3",
"echarts": "^5.0.2",
"eva-icons": "^1.1.3",
"file-saver": "^2.0.5",
"http-server": "^0.12.3",
"jquery": "^3.5.1",
"keen-slider": "^5.3.4",
"ng-recaptcha": "^6.1.0",
"ngx-echarts": "^6.0.1",
"ngx-pinch-zoom": "^2.5.4",
"ngx-typed-js": "^2.0.2",
"ngx-webcam": "^0.3.2",
"pdf-lib": "^1.12.0",
"pdfjs-dist": "^2.5.207",
"popper.js": "^1.16.1",
"pwacompat": "^2.0.17",
"resize-observer-polyfill": "^1.5.1",
"rxjs": "~6.6.0",
"signature_pad": "^2.3.2",
"tslib": "^2.0.0",
"zone.js": "~0.10.2"
},
"devDependencies": {
"@angular-devkit/build-angular": "~0.1102.6",
"@angular/cli": "~11.2.6",
"@angular/compiler-cli": "~11.2.7",
"@schematics/angular": "~10.2.0",
"@types/jasmine": "~3.6.0",
"@types/jasminewd2": "~2.0.3",
"@types/jquery": "^3.5.4",
"@types/node": "^12.20.5",
"@types/pdfjs-dist": "^2.1.7",
"codelyzer": "^6.0.0",
"jasmine-core": "~3.6.0",
"jasmine-spec-reporter": "~5.0.0",
"karma": "~6.3.2",
"karma-chrome-launcher": "~3.1.0",
"karma-coverage-istanbul-reporter": "~3.0.2",
"karma-jasmine": "~4.0.0",
"karma-jasmine-html-reporter": "^1.5.0",
"protractor": "~7.0.0",
"ts-node": "~8.3.0",
"tslint": "~6.1.0",
"typescript": "~4.0.2"
}
```