Fix GNUmake (#161)

Author: kngott

ExampleCodes/Basic/HeatEquation_EX0_C/Exec/GNUmakefile

@@ -11,7 +11,7 @@ include $(AMREX_HOME)/Tools/GNUMake/Make.defs
 
 include ../Source/Make.package
 VPATH_LOCATIONS  += ../Source
-INCLUDE_LOCATIONS += ./Source
+INCLUDE_LOCATIONS += ../Source
 
 include $(AMREX_HOME)/Src/Base/Make.package