Update Makefile

Co-authored-by: Tim Ansell <me@mith.ro>
diff --git a/Makefile b/Makefile
index 7dbe963..baee58f 100644
--- a/Makefile
+++ b/Makefile
@@ -53,7 +53,7 @@
 .PHONY: check-licenses
 
 lint-python:
-	flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+	$(IN_CONDA_ENV) flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
 
 .PHONY: lint-python