net/http/pprof: use "curl" instead of "wget" in usage example
net/http/pprof: use "curl" instead of "wget" in usage example

The "curl" binary is already used at several other places inside
the code base, whereas this was the only occurrence of "wget".

Change-Id: I2b9c5c353d08b3ba8289819b4a602c51f1ebd593
GitHub-Last-Rev: abf94855223c4ceac08dd0d18c5a2b97d1abcca9
GitHub-Pull-Request: golang/go#48718
Reviewed-on: https://go-review.googlesource.com/c/go/+/353401
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

cloudflare/go,CAFxX/go,nawawi/go,CAFxX/go,golang/go,cloudflare/go,CAFxX/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,cloudflare/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,golang/go,CAFxX/go,golang/go,nawawi/go,nawawi/go