TabMenu adds space when there is no icon

[filipvh]

[x] bug report
[ ] feature request
[ ] support request

Current behavior
primeng/src/app/components/tabmenu/tabmenu.ts
if there is no icon defined
the label is not in center
this should not be

Expected behavior
No icon -> no space on the left side of the label

Minimal reproduction of the problem with instructions
Make TabMenu Tab without icon defined

What is the motivation / use case for changing the behavior?
Normal Usage

• Angular version: 4.2.4
• PrimeNG version: 4.2.1
• Browser: [ Chrome (tested) ]
• Language:[all]