Split roundtrip_test and leakcheck.

CI status became green even if roundtrip_test failed, since `then` block
was not suspended when $? was non-zero. Splitting roundtrip_test and
leakcheck addresses this problem.

With this change, builds checks ``${TRAVIS_OS_NAME}`` twice, but
checking a variable is cheap enough.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
diff --git a/.travis.yml b/.travis.yml
index 5de5632..5ffc63b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -29,6 +29,10 @@
  - |
      if [ ${TRAVIS_OS_NAME:-'linux'} = 'linux' ]
      then
-         make roundtrip_test
-         make leakcheck
+        make roundtrip_test
+     fi
+ - |
+     if [ ${TRAVIS_OS_NAME:-'linux'} = 'linux' ]
+     then
+        make leakcheck
      fi