Update concepts-certificates.md

{{< highlight bash  >}} doesn't render properly on the wiki, so converted to codeblock

docs/src/content/concepts-certificates.md

@@ -117,26 +117,26 @@ file roughly looks like this:
 For example, you can generate a certificate in this format using these
 instructions:
 
-{{< highlight bash  >}}
+```
 openssl genrsa -out cert.key 2048
 # (Specify the mitm domain as Common Name, e.g. \*.google.com)
 openssl req -new -x509 -key cert.key -out cert.crt
 cat cert.key cert.crt > cert.pem
-{{< / highlight >}}
+```
 
 Now, you can run mitmproxy with the generated certificate:
 
 **For all domain names**
 
-{{< highlight bash  >}}
+```
 mitmproxy --cert *=cert.pem
-{{< / highlight >}}
+```
 
 **For specific domain names**
 
-{{< highlight bash  >}}
+```
 mitmproxy --cert *.example.com=cert.pem
-{{< / highlight >}}
+```
 
 **Note:** `*.example.com` is for all the subdomains. You can also use
 `www.example.com` for a particular subdomain.