Remove a letter

[NashAiomos]

Change "Ice Cube is a an open-source, 100% on-chain social network." to "Ice Cube is an open-source, 100% on-chain social network."

Thank you for your contribution to the IC Developer Portal. This repo contains the content for https://internetcomputer.org and the ICP Developer Documentation, https://internetcomputer.org/docs/.

If you are submitting a Pull Request for adding or changing content on the ICP Developer Documentation, please make sure that your contribution meets the following requirements:

• [ ] Follows the developer docs style guide.
• [ ] Follows the best practices and guidelines.
• [ ] New documentation pages include document tags.
• [ ] New documentation pages include SEO keywords.
• [ ] New documents are in the .mdx file format to support the previous two components.
• [ ] New documents are registered in /sidebars.js, otherwise, it will not appear in the side navigation bar.
• [ ] Make sure that the .github/CODEOWNERS file is filled with new documents that you added. This way we can ensure that future Pull Requests are reviewed by the right people.

[sa-github-api]

Dear @NashAiomos,

In order to potentially merge your code in this open-source repository and therefore proceed with your contribution, we need to have your approval on DFINITY's CLA.

If you decide to agree with it, please visit this issue and read the instructions there. Once you have signed it, re-trigger the workflow on this PR to see if your code can be merged.

— The DFINITY Foundation