Downgrade to net standard 1.2

ModernKeePassLib/Cryptography/RNGCryptoServiceProvider.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace ModernKeePassLib.Cryptography
+{
+    public class RNGCryptoServiceProvider: IDisposable
+    {
+        public void GetBytes(byte[] pb)
+        {
+            var random = new Random();
+            random.NextBytes(pb);
+        }
+
+        public void Dispose()
+        {
+        }
+    }
+}