Changed the build to run on 3 cores.

.travis.yml

@@ -38,7 +38,7 @@ script:
    - mkdir build
    - cd build
    - travis_wait 60 cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=../product -DBUILD_OSG_EXAMPLES=ON ..
-   - make install -j 4
+   - make install -j 3
 
 addons:
   coverity_scan:
@@ -59,7 +59,7 @@ addons:
 
     # The command that will be added as an argument to "cov-build" to compile your project for analysis,
     # ** likely specific to your build **
-    build_command: make -j 4
+    build_command: make -j 3
 
     # Pattern to match selecting branches that will run analysis. We recommend leaving this set to 'coverity_scan'.
     # Take care in resource usage, and consider the build frequency allowances per