incporporated code review comments

incporporated code review comments from @syohex

src/_flutter

@@ -86,6 +86,21 @@ _arguments -C -A "-*" \
             '--no-preamble[When analyzing the flutter repository, display the number of files that will be analyzed. (defaults to on)]' \
           && ret=0
         ;;
+        (assemble)
+            _arguments -C \
+            '(-h --help)'{-h,--help}'[Print this usage information.]' \
+          && ret=0
+        ;;
+        (attach)
+            _arguments -C \
+            '(-h --help)'{-h,--help}'[Print this usage information.]' \
+          && ret=0
+        ;;
+        (bash-completion)
+            _arguments -C \
+            '(-h --help)'{-h,--help}'[Print this usage information.]' \
+          && ret=0
+        ;;
         (build)
             _arguments -C \
             '1: :_build_entities' \
@@ -169,6 +184,11 @@ _arguments -C -A "-*" \
             '--no-preview-dart-2[Preview Dart 2.0 functionality. (defaults to on)]' \
           && ret=0
         ;;
+        (emulators)
+            _arguments -C \
+            '(-h --help)'{-h,--help}'[Print this usage information.]' \
+          && ret=0
+        ;;
         (format)
             _arguments -C \
             '(-h --help)'{-h,--help}'[Print this usage information.]' \
@@ -340,26 +360,6 @@ _arguments -C -A "-*" \
             '(-h --help)'{-h,--help}'[Print this usage information.]' \
           && ret=0
         ;;
-        (assemble)
-            _arguments -C \
-            '(-h --help)'{-h,--help}'[Print this usage information.]' \
-          && ret=0
-        ;;
-        (attach)
-            _arguments -C \
-            '(-h --help)'{-h,--help}'[Print this usage information.]' \
-          && ret=0
-        ;;
-        (bash-completion)
-            _arguments -C \
-            '(-h --help)'{-h,--help}'[Print this usage information.]' \
-          && ret=0
-        ;;
-        (emulators)
-            _arguments -C \
-            '(-h --help)'{-h,--help}'[Print this usage information.]' \
-          && ret=0
-        ;;
         (version)
             _arguments -C \
             '(-h --help)'{-h,--help}'[Print this usage information.]' \
@@ -380,6 +380,9 @@ _root_commands() {
   local commands;
   commands=(
     "analyze:Analyze the project's Dart code."
+    'assemble:Assemble and build flutter resources.'
+    'attach:Attach to a running application.'
+    'bash-completion:Output command line shell completion setup scripts.'
     'build:Flutter build commands.'
     'channel:List or switch flutter channels.'
     'clean:Delete the build/ directory.'
@@ -389,6 +392,7 @@ _root_commands() {
     'devices:List all connected devices.'
     'doctor:Show information about the installed tooling.'
     'drive:Runs Flutter Driver tests for the current project.'
+    'emulators:List, launch and create emulators.'
     'format:Format one or more dart files.'
     'fuchsia_reload:Hot reload on Fuchsia.'
     'help:Display help information for flutter.'
@@ -405,10 +409,6 @@ _root_commands() {
     'trace:Start and stop tracing for a running Flutter app.'
     'update-packages:Update the packages inside the Flutter repo.'
     'upgrade:Upgrade your copy of Flutter.'
-    'assemble:Assemble and build flutter resources.'
-    'attach:Attach to a running application.'
-    'bash-completion:Output command line shell completion setup scripts.'
-    'emulators:List, launch and create emulators.'
     'version:List or switch flutter versions.')
   _describe -t commands 'command' commands "$@"
 }