[flutter_tools] fix capitalization in build commands (#58842)

packages/flutter_tools/lib/src/commands/build_linux.dart

@@ -43,7 +43,7 @@ class BuildLinuxCommand extends BuildSubCommand {
   };
 
   @override
-  String get description => 'build the Linux desktop target.';
+  String get description => 'Build a Linux desktop application.';
 
   @override
   Future<FlutterCommandResult> runCommand() async {

packages/flutter_tools/lib/src/commands/build_macos.dart

@@ -44,7 +44,7 @@ class BuildMacosCommand extends BuildSubCommand {
   };
 
   @override
-  String get description => 'build the macOS desktop target.';
+  String get description => 'Build a macOS desktop application.';
 
   @override
   Future<FlutterCommandResult> runCommand() async {

packages/flutter_tools/lib/src/commands/build_web.dart

@@ -53,7 +53,7 @@ class BuildWebCommand extends BuildSubCommand {
   bool get hidden => !featureFlags.isWebEnabled;
 
   @override
-  final String description = 'build a web application bundle.';
+  final String description = 'Build a web application bundle.';
 
   @override
   Future<FlutterCommandResult> runCommand() async {

packages/flutter_tools/lib/src/commands/build_windows.dart

@@ -45,7 +45,7 @@ class BuildWindowsCommand extends BuildSubCommand {
   };
 
   @override
-  String get description => 'build the desktop Windows target.';
+  String get description => 'Build a Windows desktop application.';
 
   @visibleForTesting
   VisualStudio visualStudioOverride;