NbContextMenu not working when clicking the NbUser, throwing error in console

### Issue type

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

* [ x ] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**
followed the steps in the below
https://akveo.github.io/nebular/docs/components/context-menu/overview#nbcontextmenudirective

**Expected behavior:**
Context menu should be populated, but getting error in console.

**Steps to reproduce:**

**Related code:**

```
insert short code snippets here
```

### Other information:
ERROR:
NbContextMenuComponent.html:3 ERROR Error: StaticInjectorError(AppModule)[NbMenuComponent -> NbMenuInternalService]:
StaticInjectorError(Platform: core)[NbMenuComponent -> NbMenuInternalService]:
NullInjectorError: No provider for NbMenuInternalService!
at NullInjector.push../node_modules/@angular/core/fesm5/core.js.NullInjector.get (core.js:1062)
at resolveToken (core.js:1300)
at tryResolveToken (core.js:1244)
at StaticInjector.push../node_modules/@angular/core/fesm5/core.js.StaticInjector.get (core.js:1141)
at resolveToken (core.js:1300)
at tryResolveToken (core.js:1244)
at StaticInjector.push../node_modules/@angular/core/fesm5/core.js.StaticInjector.get (core.js:1141)
at resolveNgModuleDep (core.js:8369)
at NgModuleRef_.push../node_modules/@angular/core/fesm5/core.js.NgModuleRef_.get (core.js:9057)
at resolveDep (core.js:9422)
**npm, node, OS, Browser**
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**Angular, Nebular**
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