Update src/common-principles.md

Co-authored-by: Taylor Salo <[email protected]>

src/common-principles.md

@@ -564,7 +564,7 @@ like in the example below.
 
 Large tabular information, such as physiological recordings, MUST be stored with
 [compressed tab-delineated (TSVGZ) files](glossary.md#tsvgz-extensions) when
-so established by the specifications.
+so established by the specification.
 Rules for formatting plain-text tabular files apply to TSVGZ files with three exceptions:
 
 1.  The contents of TSVGZ files MUST be compressed with