[Rust] Bump smallvec version to 1.0 (#5621)

See servo/rust-smallvec#175 for changelog.

Author: messense

rust/flatbuffers/Cargo.toml

@@ -10,4 +10,4 @@ keywords = ["flatbuffers", "serialization", "zero-copy"]
 categories = ["encoding", "data-structures", "memory-management"]
 
 [dependencies]
-smallvec = "0.6"
+smallvec = "1.0"