remove build warning

Signed-off-by: Peter Siegmund <peter@rdkr.com>

ePaper-ESP-IDF/components/timber/include/timber.h

@@ -5,11 +5,11 @@
 
 class Timber {
  public:
-  static void tag(char* tag);
+  static void tag(const char* tag);
   static void plant(Tree tree);
   static void d(char* message);
   static void i(char* message);
   static void w(char* message);
   static void e(char* message);
   static void v(char* message);
-};
+};

ePaper-ESP-IDF/components/timber/timber.cpp

@@ -1,7 +1,7 @@
 #include "timber.h"
 #include <stdio.h>
 
-void Timber::tag(char* tag) {
+void Timber::tag(const char* tag) {
   printf("Tag: %s\n", tag);
 }