fix: Install pip-tools via requirements file (#77)

Author: Jawayria

Makefile

@@ -37,7 +37,7 @@ $(COMMON_CONSTRAINTS_TXT):
 
 upgrade: $(COMMON_CONSTRAINTS_TXT)
 	## update the requirements/*.txt files with the latest packages satisfying requirements/*.in
-	pip install -q pip-tools
+	pip install -qr requirements/pip-tools.txt
 	pip-compile --rebuild --upgrade --allow-unsafe -o requirements/pip.txt requirements/pip.in
 	pip-compile --rebuild --upgrade -o requirements/pip-tools.txt requirements/pip-tools.in
 	pip install -qr requirements/pip.txt