Update Dockerfile

Dockerfile

@@ -1,6 +1,6 @@
 FROM ubuntu:16.04
 
-# Install Python 3.5 and basic tools
+# Install Python 3.4 and basic tools
 RUN apt-get update && apt-get install -y \
     software-properties-common \
     wget \
@@ -17,22 +17,22 @@ RUN apt-get update && apt-get install -y \
     pkg-config \
     graphviz \
     openjdk-8-jdk \
-    python3.5 \
-    python3.5-dev \
+    python3.4 \
+    python3.4-dev \
     python3-pip \
     ant \
     ca-certificates \
     && apt-get clean \
     && update-ca-certificates -f
 
-# Install a pip version compatible with Python 3.5
-RUN python3.5 -m pip install --upgrade "pip<21.0"
+# Install a pip version compatible with Python 3.4
+RUN python3.4 -m pip install --upgrade "pip<21.0"
 
 # Copy requirements file
 COPY requirements.txt /tmp/requirements.txt
 
 # Install Python dependencies
-RUN python3.5 -m pip install --no-cache-dir -r /tmp/requirements.txt
+RUN python3.4 -m pip install --no-cache-dir -r /tmp/requirements.txt
 
 # Create a new user
 RUN useradd -m -u ${NB_UID} ${NB_USER}