Removed the bounds for the Default impl for Command (#215) #904

Job	Run time
Clippy	51s
Rustfmt	14s
Build docs	2m 33s
Test (MSRV)	5m 13s
Test (stable)	2m 3s
Test (beta)	2m 6s
Test (nightly)	2m 5s
Test (macOS)	3m 37s
Test (Windows)	3m 57s
Test (no features)	1m 14s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 17s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 22s
	26m 32s

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