Update ark-ec requirement from 0.3 to 0.4

Updates the requirements on [ark-ec](https://github.com/arkworks-rs/algebra) to permit the latest version.
- [Release notes](https://github.com/arkworks-rs/algebra/releases)
- [Changelog](https://github.com/arkworks-rs/algebra/blob/master/CHANGELOG.md)
- [Commits](arkworks-rs/algebra@v0.3.0...v0.4.2)

---
updated-dependencies:
- dependency-name: ark-ec
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Cargo.toml

@@ -13,7 +13,7 @@ sha3 = { version = "0.10", default-features = false, features = ["std", "asm"] }
 thiserror = "1"
 groth-sahai = { git = "https://github.com/jdwhite48/groth-sahai-rs" }
 ark-bls12-381 = { version = "0.3" }
-ark-ec = { version = "0.3", default-features = false }
+ark-ec = { version = "0.4", default-features = false }
 ark-ff = { version = "0.3", default-features = false }
 ark-serialize = { version = "0.3", default-features = false }
 rand_chacha = { version = "0.3" }