Update tmLanguage file to not be case sensitive

While convention states that Dockerfile instructions should be
written in uppercase, the engine allows them to be mixed case or in
lowercase. The tmLanguage file should tolerate this and provide
highlighting support even if instructions are not written in
uppercase.

Signed-off-by: Remy Suen <remy.suen@gmail.com>

contrib/syntax/textmate/Docker.tmbundle/Syntaxes/Dockerfile.tmLanguage

@@ -25,7 +25,7 @@
 				</dict>
 			</dict>
 			<key>match</key>
-			<string>^\s*\b(FROM)\b.*?\b(AS)\b</string>
+			<string>^\s*\b(?i:(FROM))\b.*?\b(?i:(AS))\b</string>
 		</dict>
 		<dict>
 			<key>captures</key>
@@ -42,7 +42,7 @@
 				</dict>
 			</dict>
 			<key>match</key>
-			<string>^\s*(?:(ONBUILD)\s+)?(ADD|ARG|CMD|COPY|ENTRYPOINT|ENV|EXPOSE|FROM|HEALTHCHECK|LABEL|MAINTAINER|RUN|SHELL|STOPSIGNAL|USER|VOLUME|WORKDIR)\s</string>
+			<string>^\s*(?i:(ONBUILD)\s+)?(?i:(ADD|ARG|CMD|COPY|ENTRYPOINT|ENV|EXPOSE|FROM|HEALTHCHECK|LABEL|MAINTAINER|RUN|SHELL|STOPSIGNAL|USER|VOLUME|WORKDIR))\s</string>
 		</dict>
 		<dict>
 			<key>captures</key>
@@ -59,7 +59,7 @@
 				</dict>
 			</dict>
 			<key>match</key>
-			<string>^\s*(?:(ONBUILD)\s+)?(CMD|ENTRYPOINT)\s</string>
+			<string>^\s*(?i:(ONBUILD)\s+)?(?i:(CMD|ENTRYPOINT))\s</string>
 		</dict>
 		<dict>
 			<key>begin</key>