Bump dependencies and crate version

Also add Parity as an author.

Cargo.toml

 [package]
 name = "eth-secp256k1"
-version = "0.5.7"
-authors = [ "Dawid Ciężarkiewicz <dpc@ucore.info>",
-            "Andrew Poelstra <apoelstra@wpsoftware.net>" ]
+version = "0.6.0"
+authors = [
+  "Dawid Ciężarkiewicz <dpc@ucore.info>",
+  "Andrew Poelstra <apoelstra@wpsoftware.net>",
+  "Parity Technologies <admin@parity.io>",
+]
 license = "CC0-1.0"
 homepage = "https://github.com/paritytech/rust-secp256k1/"
 repository = "https://github.com/paritytech/rust-secp256k1/"
 documentation = "https://www.wpsoftware.net/rustdoc/secp256k1/"
 description = "Fork of Rust bindings for Pieter Wuille's `libsecp256k1` library. Implements ECDSA for the SECG elliptic curve group secp256k1 and related utilities."
-keywords = [ "crypto", "ECDSA", "secp256k1", "libsecp256k1", "bitcoin" ]
+keywords = [ "crypto", "ECDSA", "secp256k1", "libsecp256k1", "bitcoin", "ethereum" ]
 readme = "README.md"
 build = "build.rs"
 
 [build-dependencies]
-cc = "1.0"
-cfg-if = "0.1"
+cc = "1.0.45"
+cfg-if = "0.1.10"
 
 [lib]
 name = "secp256k1"
@@ -26,10 +29,10 @@ default = []
 dev = ["clippy"]
 
 [dependencies]
-arrayvec = "0.4"
-clippy = {version = "0.0", optional = true}
-rand = "0.6"
+arrayvec = "0.5.1"
+clippy = { version = "0.0.302", optional = true }
+rand = "0.7.2"
 
 [dev-dependencies]
-hex-literal = "0.2"
-rand_core = "0.4.2"
+hex-literal = "0.2.1"
+rand_core = "0.5.1"