[PARQUET-1931] Bump Junit to 4.13.1 (#835)

Looks like there is a vulnerability in Junit:
https://github.com/Fokko/parquet-mr/pull/44
diff --git a/pom.xml b/pom.xml
index 6b1f3fa..a0d3e15 100644
--- a/pom.xml
+++ b/pom.xml
@@ -148,7 +148,7 @@
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
-      <version>4.12</version>
+      <version>4.13.1</version>
       <scope>test</scope>
     </dependency>
     <dependency>