build: Raising requirement for boost to be at least 1.48

This requirement matches the requirement of NFD.

Change-Id: I194a5e81018ab6569615854fa0af9d3a7af4cca8
diff --git a/.travis.yml b/.travis.yml
index 6755b23..f2ebc72 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,7 +9,7 @@
   - travis_retry sudo add-apt-repository -y ppa:named-data/ppa
   - travis_retry sudo apt-get update -qq
   - travis_retry sudo apt-get install -qq ndnx-dev
-  - travis_retry sudo apt-get install -qq libboost-all-dev
+  - travis_retry sudo apt-get install -qq libboost1.48-all-dev
   - travis_retry sudo apt-get install -qq libcrypto++-dev
   - travis_retry sudo apt-get install -qq libsqlite3-dev
 script: