reference: block-comment -> block comment

Author: tshepang

src/doc/reference.md

@@ -84,7 +84,7 @@ that does _not_ occur in the set of [keywords](#keywords).
 ## Comments
 
 Comments in Rust code follow the general C++ style of line (`//`) and
-block-comment (`/* ... */`) forms. Nested block comments are supported.
+block (`/* ... */`) comment forms. Nested block comments are supported.
 
 Line comments beginning with exactly _three_ slashes (`///`), and block
 comments beginning with exactly one repeated asterisk in the block-open