fixed typo

tikz/triangle-heron-tricky/triangle-heron-tricky.tex

@@ -37,7 +37,7 @@
 
     \draw[thick] (a) -- (b) node [black,midway,yshift=-0.2cm,sloped] {5cm};
     \draw[thick] (b) -- (c) node [black,midway,yshift=+0.2cm,sloped] {5cm};
-    \draw[thick] (a) -- (c) node [black,midway,yshift=+0.2cm,sloped] {7cm};
+    \draw[thick] (a) -- (c) node [black,midway,yshift=+0.2cm,sloped] {6cm};
 
     \draw[thick] (a) -- (d) node [black,midway,yshift=+0.2cm,sloped] {8cm};
     \draw[thick] (b) -- (d) node [black,midway,yshift=-0.2cm,sloped] {5cm};