bpo-29932: Fix small error message typos in arraymodule.c (GH-888)

Modules/arraymodule.c

@@ -1920,7 +1920,7 @@ array__array_reconstructor_impl(PyObject *module, PyTypeObject *arraytype,
 
     if (!PyType_Check(arraytype)) {
         PyErr_Format(PyExc_TypeError,
-            "first argument must a type object, not %.200s",
+            "first argument must be a type object, not %.200s",
             Py_TYPE(arraytype)->tp_name);
         return NULL;
     }
@@ -2143,7 +2143,7 @@ array_array___reduce_ex__(arrayobject *self, PyObject *value)
 
     if (!PyLong_Check(value)) {
         PyErr_SetString(PyExc_TypeError,
-                        "__reduce_ex__ argument should an integer");
+                        "__reduce_ex__ argument should be an integer");
         return NULL;
     }
     protocol = PyLong_AsLong(value);
@@ -2368,7 +2368,7 @@ array_ass_subscr(arrayobject* self, PyObject* item, PyObject* value)
     }
     else {
         PyErr_SetString(PyExc_TypeError,
-                        "array indices must be integer");
+                        "array indices must be integers");
         return -1;
     }
     if (value == NULL) {