Update .gitlab-ci.yml. create the build dir in the build stage

.gitlab-ci.yml

@@ -35,8 +35,6 @@ before_script:
   - module load LibTIFF/4.0.3-goolf-1.4.10
   - module load libpng/1.6.17-goolf-1.4.10
   - module load zlib/1.2.8-goolf-1.4.10
-  - mkdir build-ci
-  - cd build-ci
   - echo "... done running global 'before_script'."
 
 # BUILD STAGE
@@ -46,6 +44,8 @@ build:centos6.6:
   script:
   - echo "Building on CentOS 6..."
   - rm -fr build-ci/
+  - mkdir build-ci
+  - cd build-ci
   - cmake .. -DENABLE_MM=1
              -DOPEN_MM_LIBRARY=$EBROOTOPENMM/lib/libOpenMM.so
              -DOPEN_MM_PLUGIN_DIR=$EBROOTOPENMM/lib/plugins