get started: fixing references to images as png instead of svg (for d…

…ark mode), closes getify#1718

get-started/ch1.md

@@ -322,7 +322,7 @@ These misinformed claims and criticisms should be set aside. The real reason it
 Historically, scripted or interpreted languages were executed in generally a top-down and line-by-line fashion; there's typically not an initial pass through the program to process it before execution begins (see Figure 1).
 
 <figure>
-    <img src="images/fig1.svg" width="650" alt="Interpreting a script to execute it" align="center">
+    <img src="images/fig1.png" width="650" alt="Interpreting a script to execute it" align="center">
     <figcaption><em>Fig. 1: Interpreted/Scripted Execution</em></figcaption>
     <br><br>
 </figure>
@@ -332,7 +332,7 @@ In scripted or interpreted languages, an error on line 5 of a program won't be d
 Compare that to languages which do go through a processing step (typically, called parsing) before any execution occurs, as illustrated in Figure 2:
 
 <figure>
-    <img src="images/fig2.svg" width="650" alt="Parsing, compiling, and executing a program" align="center">
+    <img src="images/fig2.png" width="650" alt="Parsing, compiling, and executing a program" align="center">
     <figcaption><em>Fig. 2: Parsing + Compilation + Execution</em></figcaption>
     <br><br>
 </figure>
@@ -370,7 +370,7 @@ So what do these nitty-gritty details boil down to? Step back and consider the e
 To visualize those steps, again:
 
 <figure>
-    <img src="images/fig3.svg" width="650" alt="Steps of JS compilation and execution" align="center">
+    <img src="images/fig3.png" width="650" alt="Steps of JS compilation and execution" align="center">
     <figcaption><em>Fig. 3: Parsing, Compiling, and Executing JS</em></figcaption>
     <br><br>
 </figure>

get-started/ch3.md

@@ -385,7 +385,7 @@ The first argument to `Object.create(..)` specifies an object to link the newly
 Figure 4 shows how the three objects (`otherHomework`, `homework`, and `Object.prototype`) are linked in a prototype chain:
 
 <figure>
-    <img src="images/fig4.svg" width="200" alt="Prototype chain with 3 objects" align="center">
+    <img src="images/fig4.png" width="200" alt="Prototype chain with 3 objects" align="center">
     <figcaption><em>Fig. 4: Objects in a prototype chain</em></figcaption>
     <br><br>
 </figure>
@@ -418,7 +418,7 @@ The assignment to `topic` creates a property of that name directly on `otherHome
 Figure 5 shows the objects/properties after the assignment that creates the `otherHomework.topic` property:
 
 <figure>
-    <img src="images/fig5.svg" width="200" alt="3 objects linked, with shadowed property" align="center">
+    <img src="images/fig5.png" width="200" alt="3 objects linked, with shadowed property" align="center">
     <figcaption><em>Fig. 5: Shadowed property 'topic'</em></figcaption>
     <br><br>
 </figure>
@@ -456,7 +456,7 @@ mathHomework.study();
 The two objects `jsHomework` and `mathHomework` each prototype link to the single `homework` object, which has the `study()` function. `jsHomework` and `mathHomework` are each given their own `topic` property (see Figure 6).
 
 <figure>
-    <img src="images/fig6.svg" width="495" alt="4 objects prototype linked" align="center">
+    <img src="images/fig6.png" width="495" alt="4 objects prototype linked" align="center">
     <figcaption><em>Fig. 6: Two objects linked to a common parent</em></figcaption>
     <br><br>
 </figure>