[SemanticConventions] Replace hardcoded TFM (open-telemetry#2173)

Author: joegoldman2

src/OpenTelemetry.SemanticConventions/OpenTelemetry.SemanticConventions.csproj

@@ -1,16 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
-    <Description>OpenTelemetry Semantic Conventions</Description>
+    <TargetFramework>$(NetStandardMinimumSupportedVersion)</TargetFramework>
+    <Description>OpenTelemetry Semantic Conventions.</Description>
     <PackageTags>$(PackageTags);semantic-conventions</PackageTags>
     <MinVerTagPrefix>SemanticConventions-</MinVerTagPrefix>
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 
-  <!--Do not run Package Baseline Validation as this package has never released a stable version.
-  Remove this property once we have released a stable version and add PackageValidationBaselineVersion property.-->
+  <!-- Do not run Package Baseline Validation as this package has never released a stable version.
+  Remove this property once we have released a stable version and add PackageValidationBaselineVersion property. -->
   <PropertyGroup>
     <DisablePackageBaselineValidation>true</DisablePackageBaselineValidation>
   </PropertyGroup>
+
 </Project>