Parse Makefile as text (#397)

Author: Jenson3210

plugin/src/main/java/org/openrewrite/gradle/RewriteExtension.java

@@ -297,6 +297,7 @@ public List<String> getPlainTextMasks() {
                     "**/*.ksh",
                     "**/*.lock",
                     "**/lombok.config",
+                    "**/Makefile",
                     "**/*.md",
                     "**/*.mf",
                     "**/META-INF/services/**",