fix: update docs to reflect new go 1.17 version minimum (prometheus#1…

…0780)

The minimum go version was bumped to 1.17 in
29b5844, but the main README still
referenced go 1.16 as the minimum version required. This updates that.

I took a quick look through the other docs in the repo (ie, I did some
naive grepping), and this is the only reference I spotted.

Signed-off-by: TJ Hoplock <t.hoplock@gmail.com>

README.md

@@ -59,7 +59,7 @@ Prometheus will now be reachable at <http://localhost:9090/>.
 
 To build Prometheus from source code, You need:
 
-* Go [version 1.16 or greater](https://golang.org/doc/install).
+* Go [version 1.17 or greater](https://golang.org/doc/install).
 * NodeJS [version 16 or greater](https://nodejs.org/).
 * npm [version 7 or greater](https://www.npmjs.com/).