Fix writing errors in Makefiles

Makefile

-# makefile discription.
+# Makefile description.
 # basic build file for mruby
 
 # compiler, linker (gcc), archiver, parser generator

mrblib/Makefile

-# makefile discription.
+# Makefile description.
 # basic build file for mruby library (Ruby part)
 
 # project-specific macros

src/Makefile

-# makefile discription.
+# Makefile description.
 # basic build file for mruby library
 
 # project-specific macros

test/Makefile

-# makefile discription.
-# basic build file for mruby library (Ruby part)
+# Makefile description.
+# basic build file for the mruby testing environment mrbtest
 
 # project-specific macros
 # extension of the executable-file is modifiable(.exe .out ...)

tools/mirb/Makefile

-# makefile discription.
+# Makefile description.
 # basic build file for mirb executable
 
 # project-specific macros

tools/mrbc/Makefile

-# makefile discription.
+# Makefile description.
 # basic build file for mruby-compiler
 
 # project-specific macros

tools/mruby/Makefile

-# makefile discription.
+# Makefile description.
 # basic build file for mruby executable
 
 # project-specific macros