chore: update ron to 0.12 (#819)

I made this update as part of updating `ron` in Debian and thought that
you might like to have it upstream :)

Author: wetneb

Cargo.lock

@@ -48,7 +48,7 @@ csv = { version = "1.1.6", optional = true }
 console = { version = "0.15.4", optional = true, default-features = false }
 pest = { version = "2.1.3", optional = true }
 pest_derive = { version = "2.1.0", optional = true }
-ron = { version = "0.7.1", optional = true }
+ron = { version = "0.12.0", optional = true }
 toml = { version = "0.5.7", optional = true }
 globset = { version = ">= 0.4.6, < 0.4.17", optional = true }
 walkdir = { version = "2.3.1", optional = true }

insta/Cargo.toml

@@ -1,5 +1,7 @@
 use serde::de::value::Error as ValueError;
 use serde::Serialize;
+#[cfg(feature = "ron")]
+use std::borrow::Cow;
 
 use crate::content::{json, yaml, Content, ContentSerializer};
 use crate::settings::Settings;
@@ -61,19 +63,19 @@ pub fn serialize_content(mut content: Content, format: SerializationFormat) -> S
         }
         #[cfg(feature = "ron")]
         SerializationFormat::Ron => {
-            let mut buf = Vec::new();
+            let mut buf = String::new();
             let mut config = ron::ser::PrettyConfig::new();
-            config.new_line = "\n".to_string();
-            config.indentor = "  ".to_string();
+            config.new_line = Cow::Borrowed("\n");
+            config.indentor = Cow::Borrowed("  ");
             config.struct_names = true;
             let mut serializer = ron::ser::Serializer::with_options(
                 &mut buf,
                 Some(config),
-                ron::options::Options::default(),
+                &ron::options::Options::default(),
             )
             .unwrap();
             content.serialize(&mut serializer).unwrap();
-            String::from_utf8(buf).unwrap()
+            buf
         }
         #[cfg(feature = "toml")]
         SerializationFormat::Toml => {