change to beta cause master is has dart 2.9.16 for some reason

Author: danylo-safonov-solid

scripts/Dockerfile

@@ -12,5 +12,5 @@ RUN apt-get update -y \
     && rm -rf /var/lib/apt/lists/*
 
 # Installing Flutter
-RUN git clone -b stable --depth 1 https://github.com/flutter/flutter.git /flutter \
+RUN git clone -b stable --depth 1 https://github.com/flutter/flutter.git /beta \
     && flutter --version