quote 0.3.7 is required, syn’s test uses Tokens::as_str

This only affects running tests with an old Cargo.lock file
diff --git a/Cargo.toml b/Cargo.toml
index b720700..12be265 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -19,7 +19,7 @@
 fold = []
 
 [dependencies]
-quote = { version = "0.3", optional = true }
+quote = { version = "0.3.7", optional = true }
 unicode-xid = { version = "0.0.4", optional = true }
 synom = { version = "0.11", path = "synom", optional = true }