Update Dockerfile to match the app's requirements and not the example from RStudio

Dockerfile

@@ -4,10 +4,10 @@ WORKDIR /code
 
 RUN install2.r --error \
     shiny \
-    dplyr \
-    ggplot2 \
+    ellmer \
+    purrr \
     readr \
-    ggExtra
+    dplyr
     
 COPY . .