Avoid extra quotes where not strictly necessary.

It's not necessary to enclose in quotes every single string value
in log2met format; when using basic words, it's possible to not
quote it (as heroku does for its own logging). This keeps the
logs easier on the human eye.
`\w` doesn't include the dot (which is common in IP addresses, method names, etc.). 

I can avoid the regexp, but I would say that in this case it basically just contains the set of available characters. How would you change it, to a chain of conditions in ands and ors, plus a loop boolean?

```go
var invalid bool
for _,ch in range {
    if (ch >= 'a' && ch <= 'z') || (ch >='A' && ch <='Z') || (ch >= '0' || ch <'9') || ch == '-' || ch == '.') {
        invalid = true;
        break
    }
}
if invalid {
}
```
It's worse IMO, but I can change it if you want.