Fix grammar and spelling in user-facing messages

src/Hangfire.Core/AutomaticRetryAttribute.cs

@@ -378,7 +378,7 @@ private void TransitionToDeleted(ElectStateContext context, FailedState failedSt
             if (LogEvents)
             {
                 _logger.WarnException(
-                    $"Failed to process the job '{context.BackgroundJob.Id}': an exception occured. Job was automatically deleted because the retry attempt count exceeded {Attempts}.",
+                    $"Failed to process the job '{context.BackgroundJob.Id}': an exception occurred. Job was automatically deleted because the retry attempt count exceeded {Attempts}.",
                     failedState.Exception);
             }
         }

src/Hangfire.Core/Client/CoreBackgroundJobFactory.cs

@@ -113,7 +113,7 @@ private BackgroundJob CreateBackgroundJobTwoSteps(CreateContext context, Diction
                         // when its state is null, and since we shouldn't do anything when it's non-null,
                         // there will be no any race conditions.
                         var data = ctx.Context.Connection.GetJobData(ctx.BackgroundJob.Id);
-                        if (data == null) throw new InvalidOperationException($"Was unable to initialize a background job '{ctx.BackgroundJob.Id}', because it doesn't exists.");
+                        if (data == null) throw new InvalidOperationException($"Was unable to initialize a background job '{ctx.BackgroundJob.Id}', because it doesn't exist.");
 
                         if (!String.IsNullOrEmpty(data.State)) return;
                     }

src/Hangfire.Core/Dashboard/Content/resx/Strings.resx

@@ -542,7 +542,7 @@
     <value>Disabled</value>
   </data>
   <data name="RecurringJobsPage_RecurringJobDisabled_Tooltip" xml:space="preserve">
-    <value>Cron expression is invalid or don't have any occurrences over the next 100 years</value>
+    <value>Cron expression is invalid or doesn't have any occurrences over the next 100 years</value>
   </data>
   <data name="ServersPage_Note_Text" xml:space="preserve">
     <value>Some of the servers don't have heartbeat reported within the last minute and may be aborted. If they don't report heartbeat in the near future, they will be removed automatically after timeout is exceeded, no manual action is required.

src/Hangfire.Core/DisableConcurrentExecutionAttribute.cs

@@ -27,7 +27,7 @@ public class DisableConcurrentExecutionAttribute : JobFilterAttribute, IServerFi
     {
         public DisableConcurrentExecutionAttribute(int timeoutInSeconds)
         {
-            if (timeoutInSeconds < 0) throw new ArgumentException("Timeout argument value should be greater that zero.");
+            if (timeoutInSeconds < 0) throw new ArgumentException("Timeout argument value should be greater than zero.");
 
             TimeoutSec = timeoutInSeconds;
         }