Checkbox Disabled Does Not Show Visually Checked Value

[pedrotcm]

Issue type

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

• [] bug report
• feature request

Issue description

Current behavior:
The checkbox when disabled does not display the visually checked value.

Expected behavior:
Learn checkbox checked but disabled.

Steps to reproduce:
In the showcase itself in the Disabled Checkbox part.
https://akveo.github.io/nebular/docs/components/checkbox/examples#nbcheckboxcomponent

Other information:

npm, node, OS, Browser

Node v10.16.0, Npm v6.9.0
OS: Windows 10
Browser: Chrome Versão 76.0.3809.132 (Versão oficial) 64 bits

Angular, Nebular

"@angular/animations": "^8.0.0",
 "@angular/cdk": "^8.0.0",
 "@angular/common": "^8.0.0",
 "@angular/compiler": "^8.0.0",
 "@angular/core": "^8.0.0",
 "@angular/forms": "^8.0.0",
 "@angular/material": "^8.1.2",
 "@angular/platform-browser": "^8.0.0",
 "@angular/platform-browser-dynamic": "^8.0.0",
 "@angular/router": "^8.0.0",
 "@nebular/auth": "4.1.2",
 "@nebular/eva-icons": "^4.3.1",
 "@nebular/security": "4.1.2",
 "@nebular/theme": "^4.3.1",

[pedrotcm]

In fact now that I can see that it is the white color of the icon that is very close to the disabled checkbox background. I overwrote css to better fit my layout.

nb-checkbox .native-input:disabled + .custom-checkbox nb-icon { color: #abafb7; }