Update to the next version of proc-macro2

Depends on dtolnay/quote#73
Depends on alexcrichton/proc-macro2#90
Depends on a new nightly
diff --git a/src/macros.rs b/src/macros.rs
index 667c5ba..0017d50 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -133,7 +133,7 @@
 
     (($($arms:tt)*) $tokens:ident $name:ident {}) => {
         impl ::quote::ToTokens for $name {
-            fn to_tokens(&self, $tokens: &mut ::quote::Tokens) {
+            fn to_tokens(&self, $tokens: &mut ::proc_macro2::TokenStream) {
                 match *self {
                     $($arms)*
                 }