Update docs/spec/draft/source-requirements.md

Co-authored-by: Marcela Melara <marcela.melara@intel.com>
Signed-off-by: Tom Hennen <TomHennen@users.noreply.github.com>

docs/spec/draft/source-requirements.md

@@ -275,7 +275,7 @@ MAY include additional properties as asserted by the verifier.  The verifier MUS
 6.  `dependencyLevels` MAY be empty as source revisions are typically terminal nodes in a supply chain.
 
 Verifiers MAY issue these attestations based on their understanding of the underlying system (e.g. based on design docs, security reviews, etc...),
-but at SLSA Source Level 3 MUST used tamper-proof [provenance attestations](#provenance-attestations) appropriate to their SCP when making the assessment.
+but at SLSA Source Level 3 MUST use tamper-proof [provenance attestations](#provenance-attestations) appropriate to their SCP when making the assessment.
 
 The SLSA source track MAY create additional tags to include in `verifiedLevels` which attest
 to other properties of a revision (e.g. if it was code reviewed).  All SLSA source tags will start with `SLSA_SOURCE_`.