Added support for single quoted strings

Docker-DCO-1.1-Signed-off-by: Asbjorn Enge <asbjorn@hanafjedle.net> (github: asbjornenge)

contrib/syntax/textmate/Dockerfile.tmLanguage

@@ -61,6 +61,23 @@
 				</dict>
 			</array>
 		</dict>
+		<dict>
+			<key>begin</key>
+			<string>'</string>
+			<key>end</key>
+			<string>'</string>
+			<key>name</key>
+			<string>string.quoted.single.dockerfile</string>
+			<key>patterns</key>
+			<array>
+				<dict>
+					<key>match</key>
+					<string>\\.</string>
+					<key>name</key>
+					<string>constant.character.escaped.dockerfile</string>
+				</dict>
+			</array>
+		</dict>
 		<dict>
 			<key>match</key>
 			<string>^\s*#.*$</string>