[HOTFIX] downgrade breeze version to 0.7

breeze-0.8.1 causes dependency issues, as discussed in #940 .

Author: Xiangrui Meng <meng@databricks.com>

Closes #1718 from mengxr/revert-breeze and squashes the following commits:

99c4681 [Xiangrui Meng] downgrade breeze version to 0.7

mllib/pom.xml

@@ -52,7 +52,7 @@
     <dependency>
       <groupId>org.scalanlp</groupId>
       <artifactId>breeze_${scala.binary.version}</artifactId>
-      <version>0.8.1</version>
+      <version>0.7</version>
       <exclusions>
         <!-- This is included as a compile-scoped dependency by jtransforms, which is
              a dependency of breeze. -->