Fix grammar on error message

plugins/available/osx.plugin.bash

@@ -17,7 +17,7 @@ EOF
 function dock-switch() {
 
     if [ $(uname) = "Darwin" ]; then
-        
+
         if [ $1 = 3d ] ; then
             defaults write com.apple.dock no-glass -boolean NO
             killall Dock
@@ -28,10 +28,10 @@ function dock-switch() {
 
         else
             echo "usage:"
-            echo "dock-switch 2d" 
+            echo "dock-switch 2d"
             echo "dock-switch 3d."
         fi
     else
-        echo "sorry. you're currently not using os x"
+        echo "Sorry, this only works on Mac OS X"
     fi
 }