Update .appveyor.yml

.appveyor.yml

@@ -10,6 +10,7 @@ install:
         )
         [System.IO.Compression.ZipFile]::ExtractToDirectory("C:\maven-bin.zip", "C:\maven")
       }
+  - cmd: SET M2_HOME=C:\maven\apache-maven-3.2.5
   - cmd: SET PATH=C:\maven\apache-maven-3.2.5\bin;%JAVA_HOME%\bin;%PATH
   - cmd: SET MAVEN_OPTS=-XX:MaxPermSize=2g -Xmx4g
   - cmd: SET JAVA_OPTS=-XX:MaxPermSize=2g -Xmx4g