docs(select): improve naming of `c` variable in example
docs(select): improve naming of `c` variable in example

It was felt that `c` did not make it clear what the variable held. This
has been changed to `color` to match the ng-repeat expression above.
In turn the model value has been changed to `myColor` to prevent a name
collision.

Closes #7210

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js