Re-write plaforms support phrase in docs using active voice

I can't find a decent link to support this claim, but active voice is
recommended instead of passive voice in order to achieve more clarity in
writing.

Moreover, the simpler we can make our writing, the easier it will be for
non-native speakers (and native too) to understand it.

docs/architecture.md

@@ -11,8 +11,8 @@ Actually doing that though, is a bit of a process.
 `source/ci_source/providers`][provs]. These use ENV VARs to figure out which CI `danger ci` is running on and validate
 whether it is a pull request.
 
-**Step 2: Platform**. Danger needs to know which platform the code review is happening in. Today Github, Gitlab,
-BitBucket Server and BitBucket Cloud are supported. You can see them them all in [`source/platforms`][platforms].
+**Step 2: Platform**. Danger needs to know which platform the code review is happening in. Today, Danger supports
+Github, Gitlab, BitBucket Server, and BitBucket Cloud. You can see them them all in [`source/platforms`][platforms].
 
 **Step 3: JSON DSL**. To allow for all of: