observatory: change help text to match break-on-exception option name

runtime/observatory/lib/src/elements/debugger.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library debugger_page_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'observatory_element.dart';
 import 'package:observatory/app.dart';
@@ skipping 502 matching lines @@
 }
 
 class SetCommand extends DebuggerCommand {
   SetCommand(Debugger debugger)
       : super(debugger, 'set', []);
 
   static var _boeValues = ['all', 'none', 'unhandled'];
   static var _boolValues = ['false', 'true'];
 
   static var _options = {
     'break-on-exception': [_boeValues,

[Jennifer Messerly, 2015/09/02 23:22:41]

here's where the parameter is declared.
you can also see the correct name by typing "set" with no arguments, which is
how I got it working.

                            _setBreakOnException,
                            (debugger, _) => debugger.breakOnException],
     'up-is-down': [_boolValues,
                    _setUpIsDown,
                    (debugger, _) => debugger.upIsDown],
   };
 
   static Future _setBreakOnException(debugger, name, value) async {
     var result = await debugger.isolate.setExceptionPauseInfo(value);
     if (result.isError) {
@@ skipping 80 matching lines @@
     return new Future.value(result);
   }
 
   String helpShort =
       'Set a debugger option';
 
   String helpLong =
       'Set a debugger option.\n'
       '\n'
       'Known options:\n'
-      '  break-on-exceptions   # Should the debugger break on exceptions?\n'
+      '  break-on-exception    # Should the debugger break on exceptions?\n'
       "                        # ${_boeValues}\n"
       '  up-is-down            # Reverse meaning of up/down commands?\n'
       "                        # ${_boolValues}\n"
       '\n'
       'Syntax: set                    # Display all option settings\n'
       '        set <option>           # Get current value for option\n'
       '        set <option> <value>   # Set value for option';
 }
 
 class BreakCommand extends DebuggerCommand {
@@ skipping 1724 matching lines @@
         }
       });
   }
 
   void focus() {
     $['textBox'].focus();
   }
 
   DebuggerInputElement.created() : super.created();
 }