chore: fix typo

is however some --> are however some

Author: cjwyett

info.toml

@@ -295,7 +295,7 @@ path = "exercises/structs/structs2.rs"
 mode = "test"
 hint = """
 Creating instances of structs is easy, all you need to do is assign some values to its fields.
-There is however some shortcuts that can be taken when instantiating structs.
+There are however some shortcuts that can be taken when instantiating structs.
 Have a look in The Book, to find out more: https://doc.rust-lang.org/stable/book/ch05-01-defining-structs.html#creating-instances-from-other-instances-with-struct-update-syntax"""
 
 [[exercises]]