bump version of serde

Author: emizzle

ethers.nimble

@@ -9,7 +9,7 @@ requires "chronos >= 4.0.0 & < 4.1.0"
 requires "contractabi >= 0.6.0 & < 0.7.0"
 requires "questionable >= 0.10.2 & < 0.11.0"
 requires "json_rpc >= 0.4.0 & < 0.5.0"
-requires "serde#e889b76dda0636421484dcda1535aa0911345244"
+requires "serde >= v1.2.1 < 1.3.0"
 requires "stint"
 requires "stew"
 requires "eth"