Fix up Mono target framework references

Author: drewnoakes

src/NetMQ.Tests/NetMQ.Tests.csproj

@@ -20,7 +20,7 @@
     <BaseFrameworkPathOverrideForMono Condition="'$(BaseFrameworkPathOverrideForMono)' == '' AND '$(TargetIsMono)' == 'true' AND EXISTS('/usr/lib/mono')">/usr/lib/mono</BaseFrameworkPathOverrideForMono>
     <BaseFrameworkPathOverrideForMono Condition="'$(BaseFrameworkPathOverrideForMono)' == '' AND '$(TargetIsMono)' == 'true' AND EXISTS('/usr/local/lib/mono')">/usr/local/lib/mono</BaseFrameworkPathOverrideForMono>
 
-    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net47'">$(BaseFrameworkPathOverrideForMono)/4.7-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net48'">$(BaseFrameworkPathOverrideForMono)/4.8-api</FrameworkPathOverride>
 
     <!-- Add the Facades directory.  Not sure how else to do this. Necessary at least for .NET 4.5 -->
     <AssemblySearchPaths Condition="'$(BaseFrameworkPathOverrideForMono)' != ''">$(FrameworkPathOverride)/Facades;$(AssemblySearchPaths)</AssemblySearchPaths>