ci: use two parallel build jobs on Travis-CI

Change-Id: I734c5826f37e1027484ef9723933e8954dba00a8
diff --git a/.jenkins.d/01-ndn-cxx.sh b/.jenkins.d/01-ndn-cxx.sh
index 0225e2d..c9e2a63 100755
--- a/.jenkins.d/01-ndn-cxx.sh
+++ b/.jenkins.d/01-ndn-cxx.sh
@@ -42,8 +42,8 @@
 
 pushd ndn-cxx >/dev/null
 
-./waf configure -j1 --color=yes --enable-shared --disable-static --without-osx-keychain
-./waf -j1 --color=yes
+./waf configure --color=yes --enable-shared --disable-static --without-osx-keychain
+./waf build --color=yes -j${WAF_JOBS:-1}
 sudo env "PATH=$PATH" ./waf install --color=yes
 
 popd >/dev/null
diff --git a/.jenkins.d/10-build.sh b/.jenkins.d/10-build.sh
index 58bf6de..d1db270 100755
--- a/.jenkins.d/10-build.sh
+++ b/.jenkins.d/10-build.sh
@@ -11,15 +11,15 @@
 
 if [[ $JOB_NAME != *"code-coverage" && $JOB_NAME != *"limited-build" ]]; then
   # Configure/build in optimized mode with tests
-  ./waf -j1 --color=yes configure --with-tests
-  ./waf -j1 --color=yes build
+  ./waf --color=yes configure --with-tests
+  ./waf --color=yes build -j${WAF_JOBS:-1}
 
   # Cleanup
   sudo env "PATH=$PATH" ./waf --color=yes distclean
 
   # Configure/build in optimized mode without tests
-  ./waf -j1 --color=yes configure
-  ./waf -j1 --color=yes build
+  ./waf --color=yes configure
+  ./waf --color=yes build -j${WAF_JOBS:-1}
 
   # Cleanup
   sudo env "PATH=$PATH" ./waf --color=yes distclean
@@ -31,8 +31,8 @@
 elif [[ -n $BUILD_WITH_ASAN || -z $TRAVIS ]]; then
     ASAN="--with-sanitizer=address"
 fi
-./waf -j1 --color=yes configure --debug --with-tests $COVERAGE $ASAN
-./waf -j1 --color=yes build
+./waf --color=yes configure --debug --with-tests $COVERAGE $ASAN
+./waf --color=yes build -j${WAF_JOBS:-1}
 
 # (tests will be run against debug version)
 
diff --git a/.jenkins.d/README.md b/.jenkins.d/README.md
index 085e383..41812aa 100644
--- a/.jenkins.d/README.md
+++ b/.jenkins.d/README.md
@@ -32,3 +32,5 @@
 
 - `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.
+
+- `WAF_JOBS`: number of parallel build jobs used by waf, defaults to 1.
diff --git a/.travis.yml b/.travis.yml
index aeea85b..0dfe8ba 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,6 +3,7 @@
 env:
   global:
     - JOB_NAME=limited-build
+    - WAF_JOBS=2
 
 matrix:
   include: