Fix typos in plugin descriptions

[dpursehouse]

"Highlight" was misspelled as "hightlight".

[jonatkins]

Unfortunately changing the @name of a plugin breaks the update process (on desktop browsers) - hence these not being fixed,

The only safe way to fix them is to create a brand new plugin file with the fixed name, and replace the existing file with a deleted stub header. And even then, users will need to install the new version with the fixed name.