fixed content type value

lib/single-file/single-file-browser.js

@@ -24,7 +24,7 @@ this.SingleFile = this.SingleFile || (() => {
 
 	const ONE_MB = 1024 * 1024;
 	const DEBUG = false;
-	const PREFIX_DATA_URI_TEXT = "data:text/";
+	const PREFIX_CONTENT_TYPE_TEXT = "text/";
 
 	// --------
 	// Download
@@ -103,7 +103,7 @@ this.SingleFile = this.SingleFile || (() => {
 					return "data:base64,";
 				}
 			} else {
-				if (!contentType.startsWith(PREFIX_DATA_URI_TEXT)) {
+				if (!contentType.startsWith(PREFIX_CONTENT_TYPE_TEXT)) {
 					return "";
 				}
 				if (!charSet) {