ci: Update Travis-CI to use Ubuntu Linux 14.04 (trusty) and OS X 10.9 VMs

Due to resource constraints, this commit also makes Travis-CI to build
only once (debug, without precompiled headers, with tests).

Change-Id: I65ec64bca545093efae384dd00b51bbeaf7d9b65
Refs: #3360
diff --git a/.jenkins.d/README.md b/.jenkins.d/README.md
index 3bacba8..b1a3fbf 100644
--- a/.jenkins.d/README.md
+++ b/.jenkins.d/README.md
@@ -28,6 +28,7 @@
 
   * empty: default build process
   * `code-coverage` (Linux OS is assumed): build process with code coverage analysis
+  * `limited-build`: only a single build with tests
 
 - `CACHE_DIR`: the variable defines a path to folder containing cached files from previous builds,
   e.g., a compiled version of ndn-cxx library.  If not set, `/tmp` is used.