Suppress blocks_in_if_conditions clippy lint

This code is fine. Clippy's suggestion is not better.

    error: in an `if` condition, avoid complex blocks or closures with blocks; instead, move the block or closure higher and bind it with a `let`
       --> src/de.rs:990:5
        |
    990 | /     if {
    991 | |         let v = v.trim_start_matches(&['-', '+'][..]);
    992 | |         v.len() > 1 && v.starts_with('0') && v.bytes().all(|b| b.is_ascii_digit())
    993 | |     } {
        | |_____^
        |
        = note: `-D clippy::blocks-in-if-conditions` implied by `-D clippy::all`
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#blocks_in_if_conditions
    help: try
        |
    990 ~     let res = {
    991 +         let v = v.trim_start_matches(&['-', '+'][..]);
    992 +         v.len() > 1 && v.starts_with('0') && v.bytes().all(|b| b.is_ascii_digit())
    993 ~     }; if res {
        |

src/lib.rs

@@ -84,6 +84,7 @@
     clippy::redundant_else,
     clippy::single_match_else,
     // code is acceptable
+    clippy::blocks_in_if_conditions,
     clippy::cast_possible_wrap,
     clippy::cast_precision_loss,
     clippy::doc_markdown,