Fixes vertical alignment in feed tab bar (#974)

The tab bar items need `justify-content: center` on them or else they can appear unaligned when a feed name has an emoji character in it.

src/view/com/pager/TabBar.tsx

@@ -109,6 +109,7 @@ const styles = isDesktopWeb
         paddingHorizontal: 10,
         borderBottomWidth: 3,
         borderBottomColor: 'transparent',
+        justifyContent: 'center'
       },
     })
   : StyleSheet.create({
@@ -129,5 +130,6 @@ const styles = isDesktopWeb
         paddingHorizontal: isMobileWeb ? 8 : 0,
         borderBottomWidth: 3,
         borderBottomColor: 'transparent',
+        justifyContent: 'center'
       },
     })