doc: fix incorrect name in report docs

In diagnostic reports, the CPUs are listed in a "cpus" field.
This commit fixes the docs, which refer to the field as "osCpus"

PR-URL: nodejs#28830
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

doc/api/report.md

@@ -63,7 +63,7 @@ is provided below for reference.
     "osRelease": "3.10.0-862.el7.x86_64",
     "osVersion": "#1 SMP Wed Mar 21 18:14:51 EDT 2018",
     "osMachine": "x86_64",
-    "osCpus": [
+    "cpus": [
       {
         "model": "Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz",
         "speed": 2700,