L1-273: Backport genesis builder fix (paritytech#11)

Author: Marcin-Radecki

substrate/primitives/genesis-builder/Cargo.toml

@@ -19,7 +19,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 sp-api = { path = "../api", default-features = false }
 sp-runtime = { path = "../runtime", default-features = false }
 sp-std = { path = "../std", default-features = false }
-serde_json = { version = "1.0.111", default-features = false, features = ["alloc"] }
+serde_json = { version = "1.0.111", default-features = false, features = ["alloc", "arbitrary_precision"] }
 
 [features]
 default = ["std"]