Increase SixLabors.Shapes.Text netstandard target from 1.1 to 1.3

src/SixLabors.Shapes.Text/SixLabors.Shapes.Text.csproj

@@ -6,7 +6,7 @@
         <VersionPrefix Condition="$(packageversion) != ''">$(packageversion)</VersionPrefix>
         <VersionPrefix Condition="$(packageversion) == ''">0.1.0-alpha1</VersionPrefix>
         <Authors>Six Labors and contributors</Authors>
-        <TargetFrameworks>netstandard1.1;netstandard2.0</TargetFrameworks>
+        <TargetFrameworks>netstandard1.3;netstandard2.0</TargetFrameworks>
         <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
         <AssemblyName>SixLabors.Shapes.Text</AssemblyName>