Reduce warnings "mismatched indentations" on ruby 2.6

.travis.yml

@@ -4,7 +4,7 @@ cache: bundler
 
 bundler_args: --without local_development
 before_install:
-  - gem update bundler
+  - gem install bundler
 
 script: bundle exec rake
 
@@ -27,6 +27,7 @@ rvm:
 env:
   global:
     - JRUBY_OPTS="--server -J-Xms1500m -J-Xmx1500m -J-XX:+UseConcMarkSweepGC -J-XX:-UseGCOverheadLimit -J-XX:+CMSClassUnloadingEnabled"
+    - RUBYOPT="-w"
   matrix:
     - MBCHARS=activesupport
     - MBCHARS=builtin

lib/mail/multibyte/unicode.rb

@@ -302,16 +302,16 @@ def normalize(string, form=nil)
         # See http://www.unicode.org/reports/tr15, Table 1
         codepoints = u_unpack(string)
         case form
-          when :d
-            reorder_characters(decompose_codepoints(:canonical, codepoints))
-          when :c
-            compose_codepoints(reorder_characters(decompose_codepoints(:canonical, codepoints)))
-          when :kd
-            reorder_characters(decompose_codepoints(:compatability, codepoints))
-          when :kc
-            compose_codepoints(reorder_characters(decompose_codepoints(:compatability, codepoints)))
-          else
-            raise ArgumentError, "#{form} is not a valid normalization variant", caller
+        when :d
+          reorder_characters(decompose_codepoints(:canonical, codepoints))
+        when :c
+          compose_codepoints(reorder_characters(decompose_codepoints(:canonical, codepoints)))
+        when :kd
+          reorder_characters(decompose_codepoints(:compatability, codepoints))
+        when :kc
+          compose_codepoints(reorder_characters(decompose_codepoints(:compatability, codepoints)))
+        else
+          raise ArgumentError, "#{form} is not a valid normalization variant", caller
         end.pack('U*')
       end