Revert "fix: Correct pip install command in utils Dockerfile"

This reverts commit a2eeffc.

utils/Dockerfile

@@ -11,15 +11,15 @@ ENV PYTHONUNBUFFERED=1
 # We re-install binutils at the end because Python execve(2)s ld(1) to
 # load zeromq.
 
-RUN     PIP_INSTALL="pip --no-cache install"				\
+RUN     PIP="pip --no-cache install"					\
   APK_ADD="apk add --no-cache";					\
   $APK_ADD --virtual .build-deps gcc python3-dev			\
   libffi-dev musl-dev make		\
   && $APK_ADD libsodium-dev libsecp256k1-dev gmp-dev			\
   && $APK_ADD zeromq-dev findmnt						\
-  && $PIP_INSTALL base58 pynacl					\
-  && $PIP_INSTALL mnemonic pytezos requests				\
-  && $PIP_INSTALL pyblake2 pysodium flask \
+  && $PIP install base58 pynacl					\
+  && $PIP install mnemonic pytezos requests				\
+  && $PIP install pyblake2 pysodium flask \
   && apk del .build-deps \
   && $APK_ADD jq netcat-openbsd curl binutils \
   && $APK_ADD lz4