Rename isCygwin() to isXterm()

Strictly speaking this method does not check for Cygwin (as it e.g. does
not check to be on Windows) but only for XTerm (which in conjunction
with being on Windows is a sign of running under Cygwin).

Simplify the code a bit to get rid of the explicit null check long the
way.

jansi/src/main/java/org/fusesource/jansi/AnsiConsole.java

@@ -85,7 +85,7 @@ public static OutputStream wrapOutputStream(final OutputStream stream, int filen
         }
 
         String os = System.getProperty("os.name");
-        if (os.startsWith("Windows") && !isCygwin()) {
+        if (os.startsWith("Windows") && !isXterm()) {
 
             // On windows we know the console does not interpret ANSI codes..
             try {
@@ -107,7 +107,7 @@ public static OutputStream wrapOutputStream(final OutputStream stream, int filen
             // If we can detect that stdout is not a tty.. then setup
             // to strip the ANSI sequences..
             int rc = isatty(fileno);
-            if (!isCygwin() && !forceColored && rc == 0) {
+            if (!isXterm() && !forceColored && rc == 0) {
                 return new AnsiOutputStream(stream);
             }
 
@@ -129,9 +129,8 @@ public void close() throws IOException {
         };
     }
 
-    private static boolean isCygwin() {
-        String term = System.getenv("TERM");
-        return term != null && term.equals("xterm");
+    private static boolean isXterm() {
+        return "xterm".equals(System.getenv("TERM"));
     }
 
     /**