Fix punctuation

editions/tw5.com/tiddlers/howtos/Upgrading.tid

@@ -20,7 +20,7 @@ When upgrading, please remember the [[The First Rule of Using TiddlyWiki]]:
 
 This process will work on most desktop browsers. Note that none of your personal data leaves your browser with this process.
 
-# Locate your TiddlyWiki file in the file system (ie using Windows Explorer, the Finder on Mac OS X, or your file manager on Linux)
+# Locate your TiddlyWiki file in the file system (i.e. using Windows Explorer, the Finder on Mac OS X, or your file manager on Linux)
 # Visit http://tiddlywiki.com/upgrade.html in your browser
 
 # Drag your old TiddlyWiki HTML file into the browser window