Add Safe to Decimals (#814)

Author: shargon

src/Neo.SmartContract.Framework/Nep11Token.cs

@@ -31,6 +31,7 @@ public abstract class Nep11Token<TokenState> : TokenContract
         protected const byte Prefix_Token = 0x03;
         protected const byte Prefix_AccountToken = 0x04;
 
+        [Safe]
         public sealed override byte Decimals() => 0;
 
         [Safe]