Set trueColour flag to 1 instead of 255

It turns out some server implementations (namely VMware ESXi 6.5) expect
1 as the only non-zero value for the SetPixelFormat message whereas the protocol
states every non-zero value is valid
(https://github.com/rfbproto/rfbproto/blob/master/rfbproto.rst#setpixelformat).

Anyway, setting this to 1 shouldn't hurt.

Fixes #141

libvncclient/vncviewer.c

@@ -280,7 +280,7 @@ rfbClient* rfbGetClient(int bitsPerSample,int samplesPerPixel,
   client->format.depth = bitsPerSample*samplesPerPixel;
   client->appData.requestedDepth=client->format.depth;
   client->format.bigEndian = *(char *)&client->endianTest?FALSE:TRUE;
-  client->format.trueColour = TRUE;
+  client->format.trueColour = 1;
 
   if (client->format.bitsPerPixel == 8) {
     client->format.redMax = 7;