Use #[panic_implementation] attribute that was landed in the recent nightly (#199)

* Use [panic_implementation] instead of lang item

* Rebuild binaries.

polkadot/runtime/wasm/Cargo.lock

@@ -6,6 +6,11 @@ dependencies = [
  "nodrop 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "base58"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "bigint"
 version = "4.2.0"
@@ -68,6 +73,8 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "ed25519"
 version = "0.1.0"
 dependencies = [
+ "base58 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "blake2-rfc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)",
  "hex-literal 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "ring 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "substrate-primitives 0.1.0",
@@ -832,6 +839,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [metadata]
 "checksum arrayvec 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)" = "a1e964f9e24d588183fcb43503abda40d288c8657dfc27311516ce2f05675aef"
+"checksum base58 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5024ee8015f02155eee35c711107ddd9a9bf3cb689cf2a9089c97e79b6e1ae83"
 "checksum bigint 4.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5442186ef6560f30f1ee4b9c1e4c87a35a6879d3644550cc248ec2b955eb5fcd"
 "checksum bitflags 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b3c30d3802dfb7281680d6285f2ccdaa8c2d8fee41f93805dba5c4cf50dc23cf"
 "checksum blake2-rfc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)" = "5d6d530bdd2d52966a6d03b7a964add7ae1a288d25214066fd4b600f0f796400"