Increase Minimum Version of Visual Studio to 15.3.0

HtmlAbstractions.sln

@@ -1,7 +1,7 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
 VisualStudioVersion = 15.0.26127.0
-MinimumVisualStudioVersion = 10.0.40219.1
+MinimumVisualStudioVersion = 15.0.26730.03
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{A5A15F1C-885A-452A-A731-B0173DDBD913}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "test", "test", "{F31FF137-390C-49BF-A3BD-7C6ED3597C21}"