minor grammatical fixes and such

Thought I'd offer fixes for a few minor grammatical mistakes I found when reading over Do Things (which is a great read, btw).

Here's a brief summary of the changes:
- 1.2.3 when:
 - Change `and you don't want to anything` to `and you don't want to do anything`
- 2.1 nil, true, false, Truthiness, Equality
 - Change `Some other languages require you use` to `Some other languages require you to use`
 - Change `You don't need to anything weird` to `You don't need anything weird`
- 2.6 Vectors
 - Change `The next chapter explain` to `The next chapter explains`
- 2.10 Quoting
 - Change `You can also quote collections like a lists` to `You can also quote collections like lists`
- 3.3.2 Parameters
 - Change `when you provide arguments to a variable-arity functions` to `when you provide arguments to variable-arity functions`
- 3.3.3. Destructuring
 - Add `clojure` language qualifier to 2nd code block
- 3.3.5 All Functions are Created Equal
 - Change `As you program in with Clojure more` to `As you program with Clojure more`
- 4.2 let
 - Change `Missis` to `Perdita` (`Perdy` would also be acceptable ;) )