[Paper] Fix reference format
Applying
@@ -70,7 +70,7 @@ JSON data, which is then rendered in a user-interface such as the Jupyter Notebo
specification [@2016-reactive-vega-architecture], which is then parsed and executed using a reactive runtime that
internally makes use of D3.js [@2011-d3].
-The declarative nature of the Vega-Lite visualization grammar [@2005-grammar, @2017-vega-lite], and its encoding in a
+The declarative nature of the Vega-Lite visualization grammar [@2005-grammar; @2017-vega-lite], and its encoding in a
formal JSON schema, provide Altair with a number of benefits. First, much of the Altair Python code and tests are
generated from the Vega-Lite JSON schema, ensuring strict conformance with the Vega-Lite specification. Second, the JSON
data produced by Altair and consumed by Vega-Lite provides a natural serialization and file format for statistical
