Use new landing page generator

Use the new exporter-toolkit landing page generator feature.
* Update Go to 1.20.
* Update promu to 0.14.0.

Signed-off-by: SuperQ <superq@gmail.com>

.promu.yml

@@ -1,3 +1,5 @@
+go:
+    version: 1.20
 repository:
     path: github.com/prometheus-community/windows_exporter
 build:
@@ -14,5 +16,4 @@ tarball:
         - LICENSE
 crossbuild:
     platforms:
-        - windows/amd64
-        - windows/386
+        - windows