elliptic-curve: have alloc activate hybrid-array/alloc (#1982)

Enable `alloc` support for `hybrid-array` when the `alloc` crate feature
of `elliptic-curve` is enabled

Author: tarcieri

elliptic-curve/Cargo.toml

@@ -44,6 +44,7 @@ alloc = [
     "base16ct/alloc",
     "ff?/alloc",
     "group?/alloc",
+    "hybrid-array/alloc",
     "pkcs8?/alloc",
     "sec1?/alloc",
     "zeroize/alloc"