Rewrite to use GetBytes() overload available on dnxcore.

StackExchange.Redis/StackExchange/Redis/PhysicalConnection.cs

@@ -600,23 +600,20 @@ unsafe void WriteRaw(Stream stream, string value, int encodedLength)
                 stream.Write(outScratch, 0, bytes);
             }
             else
-            {
-                fixed (char* c = value)
-                fixed (byte* b = outScratch)
             {
                 int charsRemaining = value.Length, charOffset = 0, bytesWritten;
+                var valueCharArray = value.ToCharArray();
                 while (charsRemaining > Scratch_CharsPerBlock)
                 {
-                        bytesWritten = outEncoder.GetBytes(c + charOffset, Scratch_CharsPerBlock, b, ScratchSize, false);
+                    bytesWritten = outEncoder.GetBytes(valueCharArray, charOffset, Scratch_CharsPerBlock, outScratch, 0, false);
                     stream.Write(outScratch, 0, bytesWritten);
                     charOffset += Scratch_CharsPerBlock;
                     charsRemaining -= Scratch_CharsPerBlock;
                 }
-                    bytesWritten = outEncoder.GetBytes(c + charOffset, charsRemaining, b, ScratchSize, true);
+                bytesWritten = outEncoder.GetBytes(valueCharArray, charOffset, charsRemaining, outScratch, 0, true);
                 if (bytesWritten != 0) stream.Write(outScratch, 0, bytesWritten);
             }
         }
-        }
         const int ScratchSize = 512;
         static readonly int Scratch_CharsPerBlock = ScratchSize / Encoding.UTF8.GetMaxByteCount(1);
         private readonly byte[] outScratch = new byte[ScratchSize];