docs(subscriber): fix unclosed code block (#463)

Adds a missing backtick to close a code block that otherwise continued
until the end of the paragraph.

Author: crawford

console-subscriber/src/builder.rs

@@ -352,7 +352,7 @@ impl Builder {
     ///
     /// If the "env-filter" crate feature flag is enabled, the `RUST_LOG`
     /// environment variable will be parsed using the [`EnvFilter`] type from
-    /// `tracing-subscriber. If the "env-filter" feature is **not** enabled, the
+    /// `tracing-subscriber`. If the "env-filter" feature is **not** enabled, the
     /// [`Targets`] filter is used instead. The `EnvFilter` type accepts all the
     /// same syntax as `Targets`, but with the added ability to filter dynamically
     /// on span field values. See the documentation for those types for details.