CI: Tweak comments in script/screenshots.js

"should be" is unclear, does that mean this causes it to be pinned?

"assume" hopefully makes it clearer that our code is assuming it to be
true

script/screenshots.js

diff --git a/script/screenshots.js b/script/screenshots.js
index 475895c..b230a7e 100644
--- a/script/screenshots.js
+++ b/script/screenshots.js
@@ -33,15 +33,14 @@
       browserName: 'Internet Explorer',
       platform: 'Windows XP'
     },
-    pinned: true // should be pinned to IE 8
+    pinned: true // assume pinned to IE 8
   },
   {
     config: {
-      // Expecting IE 11
       browserName: 'Internet Explorer',
       platform: 'Windows 7'
     },
-    pinned: true // should be pinned to IE 11
+    pinned: true // assume pinned to IE 11
   },
   {
     config: {