Try more memory for Maven

Author: srowen

.travis.yml

@@ -2,6 +2,9 @@ language: java
 sudo: false
 install: mvn ${SPARK} ${JAVA} ${SCALA} -Dmaven.javadoc.skip=true -DskipTests=true -B -V install
 script: mvn ${SPARK} ${JAVA} ${SCALA} -Dmaven.javadoc.skip=true -q -B verify
+env:
+  global:
+    - MAVEN_OPTS=-Xmx2g
 matrix:
  include:
    # Covers Java 7, Open JDK, and Spark 1.2.x