Update app version for v1.2.1

[aureliony]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 78.89%. Comparing base (b5d4f51) to head (ddfec2b).

Files	Patch %	Lines
src/main/java/seedu/address/MainApp.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #156   +/-   ##
=========================================
  Coverage     78.89%   78.89%           
  Complexity      488      488           
=========================================
  Files            72       72           
  Lines          1464     1464           
  Branches        119      119           
=========================================
  Hits           1155     1155           
  Misses          285      285           
  Partials         24       24           

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[yisiox]

LGTM