add `meridiem` function to ku locale
Kurdish `ku` locale has it's own form of meridiem texts which are:
`AM` -> `پ.ن`
`PM` -> `د.ن`
The logic of determining which should be chosen is identical
to the main logic from the library, the only change is localized
strings for each case.
Also tests are added to the corresponding locale to ensure it
gets formatted correctly.

Closes #1724
**Describe the bug**
in Kurdish language we have our version of `AM` and `PM` but because the `ku` locale isn't defining a `meridiem` function, the library will fallback to it's own version.
In Kurdish, the mapping is like this:
`AM` -> `پ.ن`
`PM` -> `د.ن`

Also, We write using Arabic letters, which means we do not have the concept of case-sensitiveness

**Expected behavior**
Localized `meridiem` string as `پ.ن` and `د.ن`.

**Information**
 - Day.js Version: v1.10.0.7
 - OS: Irrelevant
 - Browser Irrelevant
 - Time zone: Irrelevant

Kurdish language is missing `meridiem` function
diff --git a/src/locale/ku.js b/src/locale/ku.js
index 5f1ce6a60..07a6b2f16 100644
--- a/src/locale/ku.js
+++ b/src/locale/ku.js
@@ -18,6 +18,7 @@ const locale = {
     LLL: 'D MMMM YYYY HH:mm',
     LLLL: 'dddd, D MMMM YYYY HH:mm'
   },
+  meridiem: hour => (hour < 12 ? 'پ.ن' : 'د.ن'),
   relativeTime: {
     future: 'له‌ %s',
     past: '%s',

diff --git a/test/locale/ku.test.js b/test/locale/ku.test.js
new file mode 100644
index 000000000..d3dec4c28
--- /dev/null
+++ b/test/locale/ku.test.js
@@ -0,0 +1,20 @@
+import MockDate from 'mockdate'
+import dayjs from '../../src'
+import '../../src/locale/ku'
+
+beforeEach(() => {
+  MockDate.set(new Date())
+})
+
+afterEach(() => {
+  MockDate.reset()
+})
+
+it('Format meridiem correctly', () => {
+  for (let i = 0; i <= 23; i += 1) {
+    const dayjsKu = dayjs()
+      .startOf('day')
+      .add(i, 'hour')
+    expect(dayjsKu.locale('ku').format('h A')).toBe(`${i % 12 || 12} ${i < 12 ? 'پ.ن' : 'د.ن'}`)
+  }
+})

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