Update peg requirement from 0.6 to 0.7

Updates the requirements on [peg](https://github.com/kevinmehall/rust-peg) to permit the latest version.
- [Release notes](https://github.com/kevinmehall/rust-peg/releases)
- [Commits](https://github.com/kevinmehall/rust-peg/compare/0.6.0...0.7.0)

Signed-off-by: dependabot[bot] <support@github.com>

lib/Cargo.toml

@@ -38,7 +38,7 @@ rio_turtle = "0.5"
 rio_xml = "0.5"
 hex = "0.4"
 nom = "6"
-peg = "0.6"
+peg = "0.7"
 siphasher = "0.3"
 lasso = {version="0.5", features=["multi-threaded", "inline-more"]}
 sophia_api = { version = "0.6.2", optional = true }