Use shorter and more obvious env var for EOL build type.

.travis.yml

@@ -50,12 +50,12 @@ matrix:
     # Build release package for LF end-of-line style text files.
     - env:
       - SCRIPT=ci_boost_release
-      - RELEASE_BUILD=LF
+      - EOL=LF
     
     # Build release package for CRLF end-of-line style text files (i.e. for Windows).
     - env:
       - SCRIPT=ci_boost_release
-      - RELEASE_BUILD=CRLF
+      - EOL=CRLF
     
     # Library requirements tests.
     - env: