update nuget package version

Author: 邹嵩

nuget/DotnetSpider.Core.nuspec

@@ -2,7 +2,7 @@
 <package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
   <metadata>
     <id>DotnetSpider.Core</id>
-    <version>2.5.0</version>
+    <version>2.5.1</version>
     <authors>[email protected];Walterwhatwater;xiaohuan0204</authors>
     <owners>[email protected]</owners>
     <iconUrl>https://github.com/zlzforever/DotnetSpider/blob/master/images/icon.png?raw=true</iconUrl>