Add missing closing quote in dependency override example (#3843)

lib/src/command/add.dart

diff --git a/lib/src/command/add.dart b/lib/src/command/add.dart
index ddd3aac..bc4c652 100644
--- a/lib/src/command/add.dart
+++ b/lib/src/command/add.dart
@@ -71,7 +71,7 @@
   * Add a git dependency:
     `$topLevelProgram pub add 'foo:{"git":"https://github.com/foo/foo"}'`
   * Add a dependency override:
-    `$topLevelProgram pub add 'override:foo:1.0.0`
+    `$topLevelProgram pub add 'override:foo:1.0.0'`
   * Add a git dependency with a path and ref specified:
     `$topLevelProgram pub add \\
       'foo:{"git":{"url":"../foo.git","ref":"<branch>","path":"<subdir>"}}'`''';

test/testdata/goldens/help_test/pub add --help.txt

diff --git a/test/testdata/goldens/help_test/pub add --help.txt b/test/testdata/goldens/help_test/pub add --help.txt
index f81cf7a..5c4f71b 100644
--- a/test/testdata/goldens/help_test/pub add --help.txt
+++ b/test/testdata/goldens/help_test/pub add --help.txt
@@ -32,7 +32,7 @@
   * Add a git dependency:
     `dart pub add 'foo:{"git":"https://github.com/foo/foo"}'`
   * Add a dependency override:
-    `dart pub add 'override:foo:1.0.0`
+    `dart pub add 'override:foo:1.0.0'`
   * Add a git dependency with a path and ref specified:
     `dart pub add \
       'foo:{"git":{"url":"../foo.git","ref":"<branch>","path":"<subdir>"}}'`