simplify get routine

Dockerfile

@@ -21,12 +21,11 @@ RUN \
 # install radarr
  radarr_tag=$(curl -sX GET "https://api.github.com/repos/Radarr/Radarr/releases" \
 	| awk '/tag_name/{print $4;exit}' FS='[""]') && \
- radarr_ver="${radarr_tag#v}" && \
  mkdir -p \
 	/opt/radarr && \
  curl -o \
  /tmp/radar.tar.gz -L \
-	"https://github.com/galli-leo/Radarr/releases/download/${radarr_tag}/Radarr.develop.${radarr_ver}.linux.tar.gz" && \
+	"https://github.com/galli-leo/Radarr/releases/download/${radarr_tag}/Radarr.develop.${radarr_tag#v}.linux.tar.gz" && \
  tar ixzf \
  /tmp/radar.tar.gz -C \
 	/opt/radarr --strip-components=1 && \