Upgrade iron to 0.6 version for Book tests (#1053)

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

book/tests/Cargo.toml

@@ -8,7 +8,7 @@ publish = false
 [dependencies]
 derive_more = "0.99"
 futures = "0.3"
-iron = "0.5"
+iron = "0.6"
 juniper = { path = "../../juniper" }
 juniper_iron = { path = "../../juniper_iron" }
 juniper_subscriptions = { path = "../../juniper_subscriptions" }