Fixes for Travis CI builds

Fixed regular expressions to skip tagged commits
Uses 2 cores for faster compilation
Uses a tag "JSBSim-trusty-v2018a" with a build number rather than the cryptic name "untagged-xxxx"

.travis.yml

@@ -9,23 +9,22 @@ notifications:
 # multiple times)
 branches:
   except:
-    - /JSBSim-*-v2018a/
-    - /untagged-*/
+    - /^JSBSim-.*-v2018a.*$/
+    - /^untagged-.*$/
 before_install:
   - pip install cython numpy pandas scipy
   - mkdir build
   - cd build
   - cmake -DCMAKE_INSTALL_PREFIX=~/ -DINSTALL_PYTHON_MODULE=ON ..
-  - make
+  - make -j2
 install:
   - make install
 script:
   - ctest -j2
 before_deploy:
   - git config --local user.name "bcoconni"
   - git config --local user.email "bcoconni@users.sourceforge.net"
-  - git tag -f JSBSim-trusty-v2018a -m "Ubuntu Trusty 14.04 - Release - x64"
-  - git push origin :refs/tags/JSBSim-trusty-v2018a
+  - git tag "JSBSim-trusty-v2018a-$TRAVIS_BUILD_NUMBER" -m "Ubuntu Trusty 14.04 - Release - x64"
 deploy:
   provider: releases
   api_key: