typo fix in core (#2987)

substrate/core/consensus/babe/src/digest.rs

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
-//! Private mplementation details of BABE digests.
+//! Private implementation details of BABE digests.
 
 use primitives::sr25519::{Public, Signature};
 use babe_primitives::BABE_ENGINE_ID;

substrate/core/consensus/babe/src/lib.rs

@@ -97,7 +97,7 @@ impl Config {
 	/// state.
 	pub fn get_or_compute<B: Block, C>(client: &C) -> CResult<Self>
 	where
-		C: AuxStore, C: ProvideRuntimeApi, C::Api: BabeApi<B>,
+		C: AuxStore + ProvideRuntimeApi, C::Api: BabeApi<B>,
 	{
 		trace!(target: "babe", "Getting slot duration");
 		match slots::SlotDuration::get_or_compute(client, |a, b| a.startup_data(b)).map(Self) {