Replace for ;; with for range int in all examples

[mattnathan]

I believe this to be more idiomatic of Go since it was introduced.

[mattnathan]

I thought I'd do a search (/for (\w+) := 0; \1 < (\d+|\w+); \1\+\+ \{/) over the other examples for places where range int could also be used and found candidates in these examples:

1. arrays L48, L49
2. goroutines L11
3. mutexes L45
4. rate limiting L47
5. select L32
6. slices L87, L90
7. stateful goroutines L76, L92

I can add these to the PR if you think it'll be useful?

[eliben]

I thought I'd do a search (/for (\w+) := 0; \1 < (\d+|\w+); \1\+\+ \{/) over the other examples for places where range int could also be used and found candidates in these examples:

1. arrays L48, L49

2. goroutines L11

3. mutexes L45

4. rate limiting L47

5. select L32

6. slices L87, L90

7. stateful goroutines L76, L92

I can add these to the PR if you think it'll be useful?

Yes, let's fold these into a single PR.

I can then review case by case to see what makes sense. I expect that most of them can be converted to the range loop. Initially I only added the new syntax to for, but now the feature has been around enough that it would make sense to replace all uses. Thanks in advance

[mattnathan]

That's done now