Update unicode-xid to unicode 12.1.0
diff --git a/Cargo.toml b/Cargo.toml
index bd7d78d..1852da8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -25,7 +25,7 @@
 rustdoc-args = ["--cfg", "procmacro2_semver_exempt"]
 
 [dependencies]
-unicode-xid = "0.1"
+unicode-xid = "0.2"
 
 [dev-dependencies]
 quote = "0.6"