Update comments to remove mesos references

pyspark-notebook/Dockerfile

@@ -15,7 +15,7 @@ RUN apt-get -y update && \
     apt-get install --no-install-recommends -y openjdk-8-jre-headless ca-certificates-java && \
     rm -rf /var/lib/apt/lists/*
 
-# Using the preferred mirror to download the file
+# Using the preferred mirror to download Spark
 RUN cd /tmp && \
     wget -q $(wget -qO- https://www.apache.org/dyn/closer.lua/spark/spark-${APACHE_SPARK_VERSION}/spark-${APACHE_SPARK_VERSION}-bin-hadoop${HADOOP_VERSION}.tgz\?as_json | \
     python -c "import sys, json; content=json.load(sys.stdin); print(content['preferred']+content['path_info'])") && \
@@ -24,7 +24,7 @@ RUN cd /tmp && \
     rm spark-${APACHE_SPARK_VERSION}-bin-hadoop${HADOOP_VERSION}.tgz
 RUN cd /usr/local && ln -s spark-${APACHE_SPARK_VERSION}-bin-hadoop${HADOOP_VERSION} spark
 
-# Spark and Mesos config
+# Configure Spark
 ENV SPARK_HOME=/usr/local/spark
 ENV PYTHONPATH=$SPARK_HOME/python:$SPARK_HOME/python/lib/py4j-0.10.7-src.zip \
     SPARK_OPTS="--driver-java-options=-Xms1024M --driver-java-options=-Xmx4096M --driver-java-options=-Dlog4j.logLevel=info" \