Replace int[n] with auto in staticArray examples.

The examples should encourage the most failsafe and DRY staticArray use.

std/array.d

@@ -391,15 +391,17 @@ if (isIterable!Iterable)
 @safe pure nothrow unittest
 {
     import std.range : only;
-    int[3] arr = only(1, 2, 3).staticArray!3;
+    auto arr = only(1, 2, 3).staticArray!3;
+    static assert(is(typeof(arr) == int[3]));
     assert(arr == [ 1, 2, 3 ]);
 }
 
 /// If the range has more than `n` elements, `staticArray` takes only `n`
 @safe pure nothrow unittest
 {
     import std.range : take, repeat;
-    int[4] arr = repeat(5).staticArray!4;
+    auto arr = repeat(5).staticArray!4;
+    static assert(is(typeof(arr) == int[4]));
     assert(arr == [ 5, 5, 5, 5 ]);
 }
 
@@ -413,7 +415,7 @@ pure unittest
     assertThrown!AssertError(only(1,2,3).staticArray!5);
 
     // extend the range to the desired length before handing it to staticArray
-    int[5] arr = only(1,2,3).chain(0.repeat).staticArray!5;
+    auto arr = only(1,2,3).chain(0.repeat).staticArray!5;
     assert(arr == [ 1, 2, 3, 0, 0 ]);
 }
 
@@ -435,7 +437,8 @@ unittest
         }
     }
 
-    int[5] arr = OpApply().staticArray!5;
+    auto arr = OpApply().staticArray!5;
+    static assert(is(typeof(arr) == int[5]));
     assert(arr == [ 0, 1, 2, 3, 4 ]);
 }