Increase version to 3.8.0-RC2 and build number to 2639.

Firmware/Configuration.h

@@ -16,8 +16,8 @@ extern uint16_t nPrinterType;
 extern PGM_P sPrinterName;
 
 // Firmware version
-#define FW_VERSION "3.8.0"
-#define FW_COMMIT_NR   2608
+#define FW_VERSION "3.8.0-RC2"
+#define FW_COMMIT_NR   2639
 // FW_VERSION_UNKNOWN means this is an unofficial build.
 // The firmware should only be checked into github with this symbol.
 #define FW_DEV_VERSION FW_VERSION_UNKNOWN