ci: use two parallel build jobs on Travis-CI

Change-Id: I734c5826f37e1027484ef9723933e8954dba00a8
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)