Use APP_VERSION to allow passing as build ARG

Dockerfile

@@ -2,7 +2,7 @@ FROM ghcr.io/linuxserver/baseimage-alpine:3.15
 
 ARG BUILD_DATE
 ARG VERSION
-ARG PTS_VERSION
+ARG APP_VERSION
 LABEL build_version="Linuxserver.io version:- ${VERSION} Build-date:- ${BUILD_DATE}"
 LABEL maintainer="aptalca"
 
@@ -20,12 +20,12 @@ RUN \
     jq \
     py3-pip && \
   echo "**** install plextraktsync ****" && \
-  if [ -z "${PTS_VERSION}" ]; then \
-    PTS_VERSION=$(curl -sL "https://pypi.python.org/pypi/PlexTraktSync/json" | jq -r '. | .info.version'); \
+  if [ -z "${APP_VERSION}" ]; then \
+    APP_VERSION=$(curl -sL "https://pypi.python.org/pypi/PlexTraktSync/json" | jq -r '. | .info.version'); \
   fi && \
   pip3 install --no-cache-dir -U pip && \
   pip install --no-cache-dir --find-links https://wheel-index.linuxserver.io/alpine-3.15/ \
-    PlexTraktSync==${PTS_VERSION} && \
+    PlexTraktSync==${APP_VERSION} && \
   echo "**** clean up ****" && \
   rm -rf \
     /tmp/* \