Obey clippy::filter_next

It was not initially clear to me why, after changing
`.filter(...).next()` to `.find(...)`, the borrow checker as of Rust
1.41.1 required me to inline `all.lines()` at this point :

    error[E0596]: cannot borrow `lines` as mutable, as it is not declared as mutable
      --> tyrga-bin/../build.rs:53:33
       |
    52 |                     let lines = all.lines();
       |                         ----- help: consider changing this to be mutable: `mut lines`
    53 |                     let wrote = lines
       |                                 ^^^^^ cannot borrow as mutable

    error: aborting due to previous error

    For more information about this error, try `rustc --explain E0596`.

but it [appears][0] that the new error is [expected][1], and that if I
had been using `.find()` previously instead of `.filter(...).next()`, I
would have seen a non-fatal "compat" lint under previous compiler
versions, leading me in the same direction.

[0]: rust-lang/rust#68729
[1]: rust-lang/rust#65785

build.rs

@@ -1,3 +1,5 @@
+#![deny(clippy::filter_next)]
+
 use std::error::Error;
 use std::fs;
 use std::path::Path;
@@ -47,10 +49,8 @@ fn main() -> Result<(), Box<dyn Error>> {
                     //     [wrote RegularFileObject[xyz/interesting/module/name/Packaged.class]]
                     // This lets us copy the .tas file to the right location alongside the .class.
                     let all = std::str::from_utf8(&output.stderr)?;
-                    let lines = all.lines();
-                    let wrote = lines
-                        .filter(|x| x.starts_with(&"[wrote"))
-                        .next()
+                    let wrote = all.lines()
+                        .find(|x| x.starts_with(&"[wrote"))
                         .expect("unexpected output from javac");
                     // Different versions of javac use different syntaxes for demarcating paths
                     let first = wrote

tyrga-lib/src/lib.rs

@@ -18,6 +18,7 @@
 #![deny(clippy::inefficient_to_string)]
 #![deny(clippy::comparison_chain)]
 #![deny(clippy::redundant_clone)]
+#![deny(clippy::filter_next)]
 
 // make macros visible to later modules
 #[macro_use]