docs: adr typo

Author: kdmccormick

docs/decisions/0021-openedx-core.rst

@@ -4,7 +4,7 @@
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-When this repo was created, it was intended to only encompass learning concepts. The content models were supposed to be read-optimized LMS-friendly representations of learning content. It was imaged that the authoring models would live elsewhere (e.g. Blockstore). That's why this was called "Learning Core".
+When this repo was created, it was intended to only encompass learning concepts. The content models were supposed to be read-optimized LMS-friendly representations of learning content. It was imagined that the authoring models would live elsewhere (e.g. Blockstore). That's why this was called "Learning Core".
 
 Over time, we realized that we actually needed to start by developing write-optimized CMS-friendly models, many of which are ideal to be also be used in LMS. We ended up with an "Authoring API" which powered the Studio-only Content Libraries feature.