Changing NbPasswordAuthStrategy validation options doesn't work.

### Issue type

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

* [x ] bug report
* [ ] feature request

### Issue description

**Current behavior:**

Basically, the validation options seem to be usuless. I'm attempting to change the default validation option for the registration form but the default validation options are still there.

**Expected behavior:**

When chaning the validation options, the validation should actually change. Validation error messages and everything.

**Steps to reproduce:**

Simply change the validation options in your **core.module.ts** .

**Related code:**

My **core.module.ts**:
```
export const NB_CORE_PROVIDERS = [
...MockDataModule.forRoot().providers,
...DATA_SERVICES,
...NbAuthModule.forRoot({

strategies: [
NbPasswordAuthStrategy.setup({
name: 'email',

token: {
class: NbAuthJWTToken,
key: 'token', // this parameter tells Nebular where to look for the token
},

baseEndpoint: 'http://localhost:3000/api',
login: {
redirect: {
success: '/',
failure: null, // stay on the same page
},
endpoint: '/auth/sign-in',
method: 'post',
},
register: {
redirect: {
success: '/',
failure: null, // stay on the same page
},
endpoint: '/auth/sign-up',
method: 'post',
},
logout: {
redirect: {
// Take the user back to the login page.
success: '/auth/login',
failure: '/auth/login',
},
endpoint: '/auth/sign-out',
method: 'post',
},
requestPass: {
endpoint: '/auth/request-pass',
method: 'post',
},
resetPass: {
endpoint: '/auth/reset-pass',
method: 'post',
},

// Change the validation options here.
validation: {
password: {
required: true,
minLength: 6,
},
email: {
required: true
},
fullName: {
required: true,
minLength: 1,
maxLength: 30,
regexp: '/\w+/g',
}

}
}),
],

...

];
```

### Other information:

**npm, node, OS, Browser**
Node version: v12.18.0
Npm version: 6.14.5
Windows 10
Chrome

**Angular, Nebular**
```
"dependencies": {
"@akveo/ng2-completer": "^9.0.1",
"@angular/animations": "^10.1.5",
"@angular/cdk": "^10.2.4",
"@angular/common": "^10.1.5",
"@angular/compiler": "^10.1.5",
"@angular/core": "^10.1.5",
"@angular/forms": "^10.1.5",
"@angular/material": "^10.2.4",
"@angular/platform-browser": "^10.1.5",
"@angular/platform-browser-dynamic": "^10.1.5",
"@angular/router": "^10.1.5",
"@asymmetrik/ngx-leaflet": "3.0.1",
"@nebular/auth": "6.2.1",
"@nebular/eva-icons": "5.0.0",
"@nebular/security": "^6.2.1",
"@nebular/theme": "^6.2.1",
"@swimlane/ngx-charts": "^13.0.2",
"angular2-chartjs": "0.4.1",
"bootstrap": "4.3.1",
"chart.js": "^2.9.3",
"ckeditor": "4.7.3",
"classlist.js": "1.1.20150312",
"core-js": "2.5.1",
"echarts": "^4.8.0",
"eva-icons": "^1.1.3",
"intl": "1.2.5",
"ionicons": "2.0.1",
"leaflet": "1.2.0",
"nebular-icons": "1.1.0",
"ng2-ckeditor": "^1.2.9",
"ng2-smart-table": "^1.6.0",
"ngx-echarts": "^4.2.2",
"node-sass": "^4.14.1",
"normalize.css": "6.0.0",
"pace-js": "1.0.2",
"roboto-fontface": "0.8.0",
"rxjs": "6.5.4",
"rxjs-compat": "6.3.0",
"socicon": "3.0.5",
"style-loader": "^1.1.3",
"tinymce": "4.5.7",
"tslib": "^2.0.0",
"typeface-exo": "0.0.22",
"web-animations-js": "^2.3.2",
"zone.js": "~0.10.2"
},
"devDependencies": {
"@angular-devkit/build-angular": "^0.1001.6",
"@angular/cli": "^10.1.6",
"@angular/compiler-cli": "^10.1.5",
"@angular/language-service": "10.1.5",
"@compodoc/compodoc": "^1.1.11",
"@fortawesome/fontawesome-free": "^5.14.0",
"@types/d3-color": "1.0.5",
"@types/jasmine": "2.5.54",
"@types/jasminewd2": "2.0.3",
"@types/leaflet": "1.2.3",
"@types/node": "^12.12.54",
"codelyzer": "^5.1.2",
"conventional-changelog-cli": "1.3.4",
"husky": "0.13.3",
"jasmine-core": "~3.5.0",
"jasmine-spec-reporter": "~5.0.0",
"karma": "~5.0.0",
"karma-chrome-launcher": "~3.1.0",
"karma-cli": "1.0.1",
"karma-coverage-istanbul-reporter": "~3.0.2",
"karma-jasmine": "~4.0.0",
"karma-jasmine-html-reporter": "^1.5.0",
"npm-run-all": "4.0.2",
"protractor": "~7.0.0",
"rimraf": "2.6.1",
"stylelint": "7.13.0",
"ts-node": "3.2.2",
"tslint": "~6.1.0",
"typescript": "4.0.3"
}
```