Glossary - Update open source - change 'working materials' to 'source files'

Author: AbcSxyZ

data/glossaries/external.yml

@@ -473,7 +473,7 @@
     Open source software is software that can be freely used, modified, and
     shared (in both modified and unmodified form) by anyone. Today the concept
     of "open source" is often extended beyond software, to represent a
-    philosophy of collaboration in which working materials are made available
+    philosophy of collaboration in which source files are made available
     online for anyone to fork, modify, discuss, and contribute to.
 - term: organization
   description: >-