Remove itertools dependency

Collecting into Vec of &str and joining may even be faster according
to benchmarks:
https://gist.github.com/green-s/fbd0d374b290781ac9b3f8ff03e3245d

src/configure.rs

@@ -8,7 +8,6 @@ mod server_params;
 use anyhow::{bail, ensure, Context as _, Result};
 use async_std::prelude::*;
 use async_std::task;
-use itertools::Itertools;
 use job::Action;
 use percent_encoding::{utf8_percent_encode, NON_ALPHANUMERIC};
 
@@ -682,7 +681,11 @@ async fn nicer_configuration_error(context: &Context, errors: Vec<ConfigurationE
         return first_err.msg.to_string();
     }
 
-    errors.iter().map(|e| e.to_string()).join("\n\n")
+    errors
+        .iter()
+        .map(|e| e.to_string())
+        .collect::<Vec<String>>()
+        .join("\n\n")
 }
 
 #[derive(Debug, thiserror::Error)]