Travis: fix the build

The Travis docs say that `$TRAVIS_BUILD_STAGE_NAME` is in "proper case" form:

> TRAVIS_BUILD_STAGE_NAME: The build stage in capitalized form, e.g. Test or Deploy. If a build does not use build stages, this variable is empty ("").

However, it looks like they made an (undocumented) change (probably a bug in their script handling) which means that the `$TRAVIS_BUILD_STAGE_NAME` name is now in the case as given, which in this case is _lowercase_.

This means that some of the comparisons are failing and the wrong things are executed for certain builds.

As I expect this to be a bug in Travis, I'm not changing the case for the comparisons at this time.
Instead I'm fixing this by inline fixing the case of the variable for the comparisons.

Refs:
* https://docs.travis-ci.com/user/environment-variables#default-environment-variables (near the bottom of the list)

Author: jrfnl

.travis.yml

@@ -108,15 +108,15 @@ before_install:
   # On stable PHPCS versions, allow for PHP deprecation notices.
   # Unit tests don't need to fail on those for stable releases where those issues won't get fixed anymore.
   - |
-    if [[ "$TRAVIS_BUILD_STAGE_NAME" != "Sniff" && "$PHPCS_VERSION" != "dev-master" && "$PHPCS_VERSION" != "n/a" ]]; then
+    if [[ "${TRAVIS_BUILD_STAGE_NAME^}" != "Sniff" && "$PHPCS_VERSION" != "dev-master" && "$PHPCS_VERSION" != "n/a" ]]; then
       echo 'error_reporting = E_ALL & ~E_DEPRECATED' >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
     fi
 
   - export XMLLINT_INDENT="    "
 
   # Set up test environment using Composer.
   - |
-    if [[ "$TRAVIS_BUILD_STAGE_NAME" != "Sniff" ]]; then
+    if [[ "${TRAVIS_BUILD_STAGE_NAME^}" != "Sniff" ]]; then
       # Remove the PHPCSDevCS dependency as it has different PHPCS requirements and would block installs.
       composer remove --dev phpcsstandards/phpcsdevcs --no-update --no-scripts
     fi
@@ -125,7 +125,7 @@ before_install:
       composer require --no-update --no-scripts squizlabs/php_codesniffer:${PHPCS_VERSION}
     fi
   - |
-    if [[ "$TRAVIS_BUILD_STAGE_NAME" == "Sniff" || $PHPCS_VERSION == "n/a" ]]; then
+    if [[ "${TRAVIS_BUILD_STAGE_NAME^}" == "Sniff" || $PHPCS_VERSION == "n/a" ]]; then
       # The sniff stage doesn't run the unit tests, so no need for PHPUnit.
       composer remove --dev phpunit/phpunit --no-update --no-scripts
     elif [[ "$PHPCS_VERSION" < "3.1.0" ]]; then