Update metadata.toml (#2340)

Improve text to look better on widgets

Author: iHiD

exercises/hello-world/metadata.toml

@@ -1,4 +1,4 @@
 title = "Hello World"
-blurb = "The classical introductory exercise. Just say \"Hello, World!\"."
+blurb = "Exercism's classic introductory exercise. Just say \"Hello, World!\"."
 source = "This is an exercise to introduce users to using Exercism"
 source_url = "https://en.wikipedia.org/wiki/%22Hello,_world!%22_program"