Remove `covariant` from `ProcessManager` (#71)

Closes #64
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ff6cd05..4a6aa64 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+#### 5.0.0
+
+* Remove the `covariant` keyword from `stderrEncoding` and `stdoutEncoding`
+  parameters.
+
 #### 4.2.4
 
 * Mark `stderrEncoding` and `stdoutEncoding` parameters as nullable again,
diff --git a/lib/src/interface/process_manager.dart b/lib/src/interface/process_manager.dart
index d99a874..f799dd9 100644
--- a/lib/src/interface/process_manager.dart
+++ b/lib/src/interface/process_manager.dart
@@ -141,9 +141,8 @@
     Map<String, String>? environment,
     bool includeParentEnvironment = true,
     bool runInShell = false,
-    // TODO(#64): Remove the `covariant` keyword.
-    covariant Encoding? stdoutEncoding = systemEncoding,
-    covariant Encoding? stderrEncoding = systemEncoding,
+    Encoding? stdoutEncoding = systemEncoding,
+    Encoding? stderrEncoding = systemEncoding,
   });
 
   /// Starts a process and runs it to completion. This is a synchronous
@@ -159,9 +158,8 @@
     Map<String, String>? environment,
     bool includeParentEnvironment = true,
     bool runInShell = false,
-    // TODO(#64): Remove the `covariant` keyword.
-    covariant Encoding? stdoutEncoding = systemEncoding,
-    covariant Encoding? stderrEncoding = systemEncoding,
+    Encoding? stdoutEncoding = systemEncoding,
+    Encoding? stderrEncoding = systemEncoding,
   });
 
   /// Returns `true` if the [executable] exists and if it can be executed.
diff --git a/pubspec.yaml b/pubspec.yaml
index ec925cc..d969c33 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: process
-version: 4.2.4
+version: 5.0.0
 description: A pluggable, mockable process invocation abstraction for Dart.
 homepage: https://github.com/google/process.dart