build+ci: Fixing boost version checking and travis script

Change-Id: I83e2c2b7b7373f00f2a57ffe6adcb9c61db2a260
diff --git a/wscript b/wscript
index c46c2d0..a66bfc4 100644
--- a/wscript
+++ b/wscript
@@ -52,9 +52,8 @@
 
     conf.check_boost(lib=boost_libs)
         
-    boost_version = conf.env.BOOST_VERSION.split('_')
-    if int(boost_version[0]) < 1 or int(boost_version[1]) < 48:
-        Logs.error ("Minimum required boost version is 1.48")
+    if conf.env.BOOST_VERSION_NUMBER < 104800:
+        Logs.error ("Minimum required boost version is 1.48.0")
         Logs.error ("Please upgrade your distribution or install custom boost libraries" +
                     " (http://redmine.named-data.net/projects/nfd/wiki/Boost_FAQ)")
         return