Adds colour help to bn and vc subcommands (#1811)

Adds coloured help to the bn and vc subcommands

beacon_node/src/cli.rs

@@ -5,6 +5,7 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
         .visible_aliases(&["b", "bn", "beacon"])
         .version(crate_version!())
         .author("Sigma Prime <contact@sigmaprime.io>")
+        .setting(clap::AppSettings::ColoredHelp)
         .about("The primary component which connects to the Ethereum 2.0 P2P network and \
                 downloads, verifies and stores blocks. Provides a HTTP API for querying \
                 the beacon chain and publishing messages to the network.")

validator_client/src/cli.rs

@@ -4,6 +4,7 @@ use clap::{App, Arg};
 pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
     App::new("validator_client")
         .visible_aliases(&["v", "vc", "validator"])
+        .setting(clap::AppSettings::ColoredHelp)
         .about(
             "When connected to a beacon node, performs the duties of a staked \
                 validator (e.g., proposing blocks and attestations).",