Update semver dev-dependency in nop-preprocessor example to 1.0

[dtolnay]

The API involved in the example is the following, none of which has changed between 0.11 and 1.0.

mdBook/examples/nop-preprocessor.rs

Line 6 in 3366406

use semver::{Version, VersionReq};

mdBook/examples/nop-preprocessor.rs

Lines 37 to 40 in 3366406

	let book_version = Version::parse(&ctx.mdbook_version)?;
	let version_req = VersionReq::parse(mdbook::MDBOOK_VERSION)?;
	if !version_req.matches(&book_version) {

[ehuss]

Thank you!