build: fix the Makefile after two header files were renamed

Reported-by: Kamil Dudka <kdudka@redhat.com>

src/Makefile.am

@@ -21,7 +21,10 @@ revision.h: FORCE
 FORCE:
 
 bin_PROGRAMS = 	nano
-nano_SOURCES =	browser.c \
+nano_SOURCES = \
+		definitions.h \
+		prototypes.h \
+		browser.c \
 		chars.c \
 		color.c \
 		cut.c \
@@ -31,9 +34,7 @@ nano_SOURCES =	browser.c \
 		history.c \
 		move.c \
 		nano.c \
-		nano.h \
 		prompt.c \
-		proto.h \
 		rcfile.c \
 		search.c \
 		text.c \