tweak the message for a missing package_config.json file (#2507)

diff --git a/lib/src/entrypoint.dart b/lib/src/entrypoint.dart
index 04a7ead..6e545fd 100644
--- a/lib/src/entrypoint.dart
+++ b/lib/src/entrypoint.dart
@@ -421,10 +421,10 @@
     }
     if (!entryExists(packageConfigFile)) {
       dataError(
-        'No .dart_tool/package_config.json file found, please run "pub get" '
-        'first.\n\n'
-        'Starting with Dart 2.7 this file configures the resolution of '
-        'package import URIs. Running "pub get" will generate this file.',
+        'No .dart_tool/package_config.json file found, please run "pub get".\n'
+        '\n'
+        'Starting with Dart 2.7, the package_config.json file configures '
+        'resolution of package import URIs; run "pub get" to generate it.',
       );
     }
     if (!entryExists(packagesFile)) {
diff --git a/test/must_pub_get_test.dart b/test/must_pub_get_test.dart
index 782a0d5..de2a503 100644
--- a/test/must_pub_get_test.dart
+++ b/test/must_pub_get_test.dart
@@ -54,7 +54,7 @@
       });
 
       _requiresPubGet(
-          'No .dart_tool/package_config.json file found, please run "pub get" first.');
+          'No .dart_tool/package_config.json file found, please run "pub get".');
     });
 
     group('the pubspec has a new dependency', () {