chore(deps): bump boto3 from 1.18.1 to 1.18.15 (#591)

Bumps [boto3](https://github.com/boto/boto3) from 1.18.1 to 1.18.15.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/boto/boto3/blob/develop/CHANGELOG.rst">boto3's changelog</a>.</em></p>
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<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/boto/boto3/commit/0b26529f157fc797880cda435d6c957b3a65c325"><code>0b26529</code></a> Merge branch 'release-1.18.15'</li>
<li><a href="https://github.com/boto/boto3/commit/afad98b2edb671ceeb81e10e7cccf2f0dc53a2a0"><code>afad98b</code></a> Bumping version to 1.18.15</li>
<li><a href="https://github.com/boto/boto3/commit/c9c7944e4bec843bef2d8c3fc67180486d027148"><code>c9c7944</code></a> Add changelog entries from botocore</li>
<li><a href="https://github.com/boto/boto3/commit/4c0e64d0d0131a676f4cd133962644ca8f6532b6"><code>4c0e64d</code></a> Merge branch 'release-1.18.14'</li>
<li><a href="https://github.com/boto/boto3/commit/c93a5e0888906ba49289c8fef740d326f1bcb5d0"><code>c93a5e0</code></a> Merge branch 'release-1.18.14' into develop</li>
<li><a href="https://github.com/boto/boto3/commit/a3f99a38cfdcd4850ae66cbc72c150b78beb0d47"><code>a3f99a3</code></a> Bumping version to 1.18.14</li>
<li><a href="https://github.com/boto/boto3/commit/e658034c1de95d2cbe1ba5514f932b39653f9636"><code>e658034</code></a> Add changelog entries from botocore</li>
<li><a href="https://github.com/boto/boto3/commit/7bcd6697a823a547a0c667ec2db3e786330f5dc5"><code>7bcd669</code></a> Merge branch 'release-1.18.13'</li>
<li><a href="https://github.com/boto/boto3/commit/ef3702f1bef540673962ed79095b34b00a3abdd3"><code>ef3702f</code></a> Merge branch 'release-1.18.13' into develop</li>
<li><a href="https://github.com/boto/boto3/commit/c25afdf8031f07fee545b74e2e9c9c9e334f1ac4"><code>c25afdf</code></a> Bumping version to 1.18.13</li>
<li>Additional commits viewable in <a href="https://github.com/boto/boto3/compare/1.18.1...1.18.15">compare view</a></li>
</ul>
</details>
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Author: dependabot[bot]