Fix build.rs in project readme (#49)

Author: StefanB7

README.md

@@ -48,12 +48,12 @@ info provided by your apps `build.rs`:
         b.freertos("path/to/FreeRTOS-Kernel");
         b.freertos_config("src");       // Location of `FreeRTOSConfig.h` 
         b.freertos_port("GCC/ARM_CM3"); // Port dir relativ to 'FreeRTOS-Kernel/portable' 
-        b.heap("heap4.c");              // Set the heap_?.c allocator to use from 
+        b.heap("heap_4.c");             // Set the heap_?.c allocator to use from 
                                         // 'FreeRTOS-Kernel/portable/MemMang' (Default: heap_4.c)       
    
         // b.get_cc().file("More.c");   // Optional additional C-Code to be compiled
     
-        b.compile().unwrap_or_else(|e| { panic!(e.to_string()) });
+        b.compile().unwrap_or_else(|e| { panic!("{}", e.to_string()) });
     }
     ```