[master] Fixed typo in the Makefile.am which caused distcheck failure.

src/lib/dhcp/Makefile.am

@@ -41,7 +41,7 @@ libkea_dhcp___la_SOURCES += option.cc option.h
 libkea_dhcp___la_SOURCES += option_custom.cc option_custom.h
 libkea_dhcp___la_SOURCES += option_data_types.cc option_data_types.h
 libkea_dhcp___la_SOURCES += option_definition.cc option_definition.h
-libkea_dhcp___la_SOURCES += option_opaque_data_tuples.cc option_opqaue_data_tuples.h
+libkea_dhcp___la_SOURCES += option_opaque_data_tuples.cc option_opaque_data_tuples.h
 libkea_dhcp___la_SOURCES += option_space.cc option_space.h
 libkea_dhcp___la_SOURCES += option_string.cc option_string.h
 libkea_dhcp___la_SOURCES += protocol_util.cc protocol_util.h