Make iOS trailing newlines not use current typing attributes (#183)

Trailing newlines on iOS need to be measured as if there was a fake `I`
character to get the proper measurement. But incorrectly, current typing
attributes were used for the character. This resulted in a funny thing;
trailing newline would change sizes if we changed selection from a, say,
heading line to non heading line. Now it uses the default typing
attributes.

Author: szydlovsky

ios/EnrichedTextInputView.mm

@@ -565,7 +565,7 @@ - (CGSize)measureSize:(CGFloat)maxWidth {
     unichar lastChar = [currentStr.string characterAtIndex:currentStr.length-1];
     if([[NSCharacterSet newlineCharacterSet] characterIsMember:lastChar]) {
       [currentStr appendAttributedString:
-        [[NSAttributedString alloc] initWithString:@"I" attributes:textView.typingAttributes]
+        [[NSAttributedString alloc] initWithString:@"I" attributes:defaultTypingAttributes]
       ];
     }
   }