Clippy: Fix "this is a decimal constant"

[duesee]

Can we fix (not silence) all "this is a decimal constant" warnings? We discussed that some weeks ago but reached no consensus. To me, writing "3" (decimal) as "03" is SO confusing. Glad that clippy lints against that :-) I would propose to just use hex notation.

this is a decimal constant

warning: this is a decimal constant
   --> simple_https_server/src/lib.rs:132:72
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132 |                         .write_record(ByteSeq::from_public_slice(&[21, 03, 03, 00, 02, 2, 47]))?;
    |                                                                        ^^
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    = note: `#[warn(clippy::zero_prefixed_literal)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#zero_prefixed_literal
help: if you mean to use a decimal constant, remove the `0` to avoid confusion
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132 |                         .write_record(ByteSeq::from_public_slice(&[21, 3, 03, 00, 02, 2, 47]))?;
    |                                                                        ~
help: if you mean to use an octal constant, use `0o`
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132 |                         .write_record(ByteSeq::from_public_slice(&[21, 0o3, 03, 00, 02, 2, 47]))?;
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