Improve documentation of travis build scripts

Author: cboehme

travis/sonarqube.sh

@@ -1,5 +1,11 @@
 #!/usr/bin/env bash
 
+#
+# Sonarqube analysis cannot be made when building pull requests because secure
+# variables are not available in such builds. To prevent build  failures, the
+# sonarqube target is only invoked if not building a pull request.
+#
+
 function main {
     require_no_pull_request
     ./gradlew sonarqube

travis/switch-to-branch.sh

@@ -2,12 +2,12 @@
 
 #
 # When building branches Travis does not check out the branch but a specific
-# commit. This results in the working copy being in "detached HEAD" state.  The
-# breaks the logic for deriving version numbers from branch names in the build
-# script.
+# commit. This results in the working copy being in "detached HEAD" state.
+# This breaks the logic for deriving version numbers from branch names in the
+# build script.
 # 
 # This script checks if the current build corresponds to the tip of a branch.
-# If it is then the branch is checked out.
+# If it does then the branch is checked out.
 #
 
 function main {