Update issue templates

.github/ISSUE_TEMPLATE/modify-existing-term.md

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+---
+name: Modify existing term
+about: Suggest a modification to an existing term
+title: "[Modify] "
+labels: invalid
+assignees: jsimonclark
+
+---
+
+**Which term do you want to modify?**
+IRI : (IRI of the proposed term to be modified)
+
+**Provide a short (max 3 sentences) justification for modifying the term.**
+A clear and concise description of why the term should be modified.
+
+**Proposed annotation property modifications**
+List all suggested modifications to annotation properties here using the style, annotationProperty --> text
+
+**Proposed data property modifications**
+List all suggested modifications to data properties here using the style, dataProperty --> value
+
+**Proposed object property modifications**
+List all suggested modifications to object properties here using the style, objectProperty --> Object
+
+**Additional context**
+Add any other context or screenshots about the feature request here.