docs: convert curl downloads from HTTP to HTTPS

Several command literals in the installation documents for downloading
used `curl` with non-HTTPS protocol.  They have been converted to HTTPS
for both man-in-the-middle risk reduction and consistency with the rest
of the documentation corpus.

docs/getting-started-guides/minikube.md

@@ -79,7 +79,7 @@ curl -Lo kubectl http://storage.googleapis.com/kubernetes-release/release/{{page
 
 The generic download path is:
 ```
-http://storage.googleapis.com/kubernetes-release/release/${K8S_VERSION}/bin/${GOOS}/${GOARCH}/${K8S_BINARY}
+https://storage.googleapis.com/kubernetes-release/release/${K8S_VERSION}/bin/${GOOS}/${GOARCH}/${K8S_BINARY}
 ```
 
 ### Starting the cluster