Fix grammar on home page by changing , to ;

I double-checked correctness of the change against the grammar rules in “Purdue OWL” – “Commas vs. Semicolons in Compound Sentences” https://owl.english.purdue.edu/owl/resource/607/04/ .

keywords: comma to semicolon
Merge pull request #2758 from roryokane/home-page-comma-to-semicolon

Fix grammar on home page by changing , to ;