Add errors stabilized in 1.34 to the core Error shims

Fixes #324

src/no_std_error.rs

@@ -25,21 +25,16 @@ macro_rules! impl_error {
 // All errors supported by our minimum suported Rust version can be supported by
 // default.
 impl_error![
-    core::str::ParseBoolError,    // 1.0
-    core::str::Utf8Error,         // 1.0
-    core::num::ParseIntError,     // 1.0
-    core::num::ParseFloatError,   // 1.0
-    core::char::DecodeUtf16Error, // 1.9
-    core::fmt::Error,             // 1.11
-    core::cell::BorrowMutError,   // 1.13
-    core::cell::BorrowError,      // 1.13
-    core::char::ParseCharError    // 1.20
-];
-
-// We can gate these together with std futures.
-#[cfg(feature = "futures")]
-impl_error![
-    core::num::TryFromIntError,     // 1.34
+    core::num::ParseFloatError,     // 1.0
+    core::num::ParseIntError,       // 1.0
+    core::str::ParseBoolError,      // 1.0
+    core::str::Utf8Error,           // 1.0
+    core::char::DecodeUtf16Error,   // 1.9
+    core::fmt::Error,               // 1.11
+    core::cell::BorrowError,        // 1.13
+    core::cell::BorrowMutError,     // 1.13
+    core::char::ParseCharError      // 1.20
     core::array::TryFromSliceError, // 1.34
     core::char::CharTryFromError    // 1.34
+    core::num::TryFromIntError,     // 1.34
 ];