Fix build issue

Author: thompson-tomo

src/CacheTower.Serializers.SystemTextJson/CacheTower.Serializers.SystemTextJson.csproj

@@ -8,7 +8,7 @@
 		<Authors>James Turner</Authors>
 	</PropertyGroup>
 
-	<ItemGroup Condition="'$(TargetFramework)' == 'netstandard6.0'">
+	<ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
 		<PackageReference Include="System.Text.Json" Version="6.0.8" />
 	</ItemGroup>
 

src/CacheTower/Internal/CacheEntryKeyLock.cs

@@ -22,7 +22,7 @@ public bool AcquireLock(string cacheKey)
 				keyLocks[cacheKey] = null;
 			}
 			return hasLock;
-#elif NETSTANDARD2_1
+#else
 			return keyLocks.TryAdd(cacheKey, null);
 #endif
 		}
@@ -56,7 +56,7 @@ private bool TryRemove(string cacheKey, out TaskCompletionSource<ICacheEntry>? c
 				return true;
 			}
 			return false;
-#elif NETSTANDARD2_1
+#else
 			return keyLocks.Remove(cacheKey, out completionSource);
 #endif
 		}

src/CacheTower/Internal/MD5HashUtility.cs

@@ -17,7 +17,7 @@ public static unsafe string ComputeHash(string value)
 		var bytes = Encoding.UTF8.GetBytes(value);
 		var hashBytes = HashAlgorithm.ComputeHash(bytes);
 
-#elif NETSTANDARD2_1
+#else
 	public static unsafe string ComputeHash(ReadOnlySpan<char> value)
 	{
 		var encoding = Encoding.UTF8;
@@ -29,9 +29,9 @@ public static unsafe string ComputeHash(ReadOnlySpan<char> value)
 		HashAlgorithm.TryComputeHash(bytes, hashBytes, out var _);
 #endif
 
-		//Based on byte conversion implementation in BitConverter (but with the dash stripped)
-		//https://github.com/dotnet/coreclr/blob/fbc11ea6afdaa2fe7b9377446d6bb0bd447d5cb5/src/mscorlib/shared/System/BitConverter.cs#L409-L440
-		static char GetHexValue(int i)
+	//Based on byte conversion implementation in BitConverter (but with the dash stripped)
+	//https://github.com/dotnet/coreclr/blob/fbc11ea6afdaa2fe7b9377446d6bb0bd447d5cb5/src/mscorlib/shared/System/BitConverter.cs#L409-L440
+	static char GetHexValue(int i)
 		{
 			if (i < 10)
 			{