v1.2.1 to fix DutyCycle bug, etc.

### Releases v1.2.1

1. Fix `DutyCycle` bug. Check [float precisison of DutyCycle only sometimes working #3](khoih-prog/SAMD_Slow_PWM#3)
2. Fix `New Period` display bug. Check [random dropouts #4](khoih-prog/SAMD_Slow_PWM#4)
3. Update examples

CONTRIBUTING.md

@@ -15,7 +15,7 @@ If you don't find anything, please [open a new issue](https://github.com/khoih-p
 Please ensure to specify the following:
 
 * Arduino IDE version (e.g. 1.8.19) or Platform.io version
-* Arduino `mbed` Core Version (e.g. Arduino `mbed` core v1.3.2 or Arduino `mbed_nano` core v2.6.1)
+* Arduino `mbed` Core Version (e.g. Arduino `mbed` core v1.3.2 or Arduino `mbed_nano` core v2.7.2)
 * Contextual information (e.g. what you were trying to achieve)
 * Simplest possible steps to reproduce
 * Anything that might be relevant in your opinion, such as:
@@ -27,9 +27,9 @@ Please ensure to specify the following:
 
 ```
 Arduino IDE version: 1.8.19
-Arduino mbed_nano` core v2.6.1
+Arduino mbed_nano` core v2.7.2
 OS: Ubuntu 20.04 LTS
-Linux xy-Inspiron-3593 5.4.0-97-generic #110-Ubuntu SMP Thu Jan 13 18:22:13 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
+Linux xy-Inspiron-3593 5.4.0-100-generic #113-Ubuntu SMP Thu Feb 3 18:43:29 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
 
 Context:
 I encountered a crash while trying to use the Timer Interrupt.