Bump prefig version to get clipping fix (#932)

* Bump prefig version to get clipping fix

* Fix duplicate label warnings

Author: siwelwerd

requirements.txt

@@ -1,5 +1,5 @@
 pretext[prefigure] == 2.36.0
-prefig >= 0.5.6
+prefig >= 0.5.7
 CodeChat-Server == 0.2.25
 pelican == 4.11.0
 markdown == 3.7.0

source/precalculus/source/06-TR/prefigure/TR5-angle2.xml

@@ -11,7 +11,7 @@
     <circle at="c" center="(0,0)" radius="1" stroke="gray" thickness="1"/>
 
     <angle-marker at="a" points="(p1,(0,0),p2)" alignment="east"><m>\alpha</m></angle-marker>
-    <angle-marker at="a" points="(p2,(0,0),p3)" alignment="northwest"><m>150^\circ</m></angle-marker>
+    <angle-marker at="b" points="(p2,(0,0),p3)" alignment="northwest"><m>150^\circ</m></angle-marker>
     <vector at="v1" v="p1" stroke="blue" thickness="2"/>
     <vector at="v2" v="p2" stroke="blue" thickness="2"/>
     <vector at="v3" v="p3" stroke="blue" thickness="2"/>

source/precalculus/source/06-TR/prefigure/TR5-point-unit-circle.xml

@@ -14,8 +14,7 @@
       <vector at="v2" v="p2" stroke="blue" thickness="2"/>
       <label color="blue" anchor="1/2*p2" alignment="northwest" ><m>r</m></label>
     </group>
-      <vector at="v2" v="p2" stroke="blue" thickness="2"/>
-      <point at="p" p="p2"><m>(x,y)</m></point>
+    <point at="p" p="p2"><m>(x,y)</m></point>
 
 
   </coordinates>