Migrate ff_derive to proc-macro2 1.0

ff/ff_derive/src/lib.rs

@@ -91,10 +91,10 @@ fn fetch_wrapped_ident(body: &syn::Data) -> Option<syn::Ident> {
 /// Fetch an attribute string from the derived struct.
 fn fetch_attr(name: &str, attrs: &[syn::Attribute]) -> Option<String> {
     for attr in attrs {
-        if let Some(meta) = attr.interpret_meta() {
+        if let Ok(meta) = attr.parse_meta() {
             match meta {
                 syn::Meta::NameValue(nv) => {
-                    if nv.ident.to_string() == name {
+                    if nv.path.get_ident().map(|i| i.to_string()) == Some(name.to_string()) {
                         match nv.lit {
                             syn::Lit::Str(ref s) => return Some(s.value()),
                             _ => {