Fix spelling mistakes

git ls-files | misspellings -f -
Source: https://github.com/lyda/misspell-check

Change-Id: I7d63578734ca5cc1ec865a7d024c1a013d1ada87
diff --git a/HACKING.rst b/HACKING.rst
index 77194a3..3fef950 100644
--- a/HACKING.rst
+++ b/HACKING.rst
@@ -174,7 +174,7 @@
   the script on non-zero exit codes::
 
     # This script exits on an error so that errors don't compound and you see
-    # only the first error that occured.
+    # only the first error that occurred.
     set -o errexit
 
     # Print the commands being run so that we can see the command that triggers