Added missing serial commas to the homepage (jupyter#664)

Author: palewire

index.html

@@ -79,7 +79,7 @@
       alt: icon to represent an interactive widget
       src: assets/homepage/widget.svg
   - headline: Big data integration
-    description: Leverage big data tools, such as Apache Spark, from Python, R and Scala. Explore that same data with pandas, scikit-learn, ggplot2, TensorFlow.
+    description: Leverage big data tools, such as Apache Spark, from Python, R, and Scala. Explore that same data with pandas, scikit-learn, ggplot2, and TensorFlow.
     image:
       alt: spark logo to represent big data
       src: assets/homepage/spark.svg
@@ -140,12 +140,12 @@
   description: Project Jupyter promotes open standards that third-party developers can leverage to build customized applications. Think HTML and CSS for interactive computing on the web.
   features:
   - headline: Notebook Document Format
-    description: Jupyter Notebooks are an open document format based on JSON. They contain a complete record of the user's sessions and include code, narrative text, equations and rich output.
+    description: Jupyter Notebooks are an open document format based on JSON. They contain a complete record of the user's sessions and include code, narrative text, equations, and rich output.
     image:
       alt: icon to represent notebook format
       src: assets/homepage/notebook-format.svg
   - headline: Interactive Computing Protocol
-    description: The Notebook communicates with computational Kernels using the Interactive Computing Protocol, an open network protocol based on JSON data over ZMQ and WebSockets.
+    description: The Notebook communicates with computational Kernels using the Interactive Computing Protocol, an open network protocol based on JSON data over ZMQ, and WebSockets.
     image:
       alt: icon to represent a protocol
       src: assets/homepage/protocol.svg