surround key name with single quotes for readability

[jakejgordon]

This is a super, super, super-duper minor change that helps with readability. I find that user input fields are sometimes hard to read and a message like:

"Calling code requested setting named but it was not in the config file. (if the appSettings key was blank)

or

Calling code requested setting named key but it was not in the config file. (in the case of a poorly named appSettings key)

Single quotes help in these cases.

[davidwhitney]

No such thing as a too-small improvement :)

I'll get the packages up on NuGet later this evening.

[jakejgordon]

Hey, thanks for a super-great and much needed package btw. I use this everywhere!