[swift-evolution] [Draft] Fix a typo in two String methods

[Andrew Trick]

> On Jul 23, 2016, at 3:16 PM, Chris Lattner <clattner at apple.com> wrote:
> 
> 
>> On Jul 23, 2016, at 2:38 PM, Andrew Trick via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>>> 
>>> On Jul 23, 2016, at 2:06 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> On Sat, Jul 23, 2016 at 3:54 PM, Daniel Duan <daniel at duan.org> wrote:
>>> In the context of character sets, "nul" is the correct name for the 0 value. "null" only makes sense when we are talking about pointer-like references.
>>> 
>>> Oh, I see: "NUL-terminated" is a thing because "NUL" is the ASCII name. Still a little bizarre looking, though, especially if it's UTF8 rather than ASCII. I am less bothered by it now, thanks :)
>> 
>> Yeah. Using the ASCII abbreviation was intentional but after thinking about it for a second I still think it should be renamed. Swift methods are supposed to be spelled out in english. There’s no reason to use an abbreviation here.
> 
> “NUL” is an abbreviation for “Null Character”.  You think that it is a good idea to spell out its full two-word name?
> https://en.wikipedia.org/wiki/Null_character

I’ll take the troll bait. “nulTerminatedUTF8" should read “nullTerminatedUTF8” because
1. null-terminated is a common english phrase
2. the acronym is not recognizable lowercase and in the context of the above phrase

Andy