Adds .make to extensions

This would enable switching out files for types in the [checkmake hook][1]

[1]: checkmake/checkmake@4e37f3a

Author: colindean

identify/extensions.py

@@ -127,6 +127,7 @@
     'lr': {'text', 'lektor'},
     'lua': {'text', 'lua'},
     'm': {'text', 'objective-c'},
+    'make': {'text', 'makefile'},
     'manifest': {'text', 'manifest'},
     'map': {'text', 'map'},
     'markdown': {'text', 'markdown'},