Strip leading newline in img.alt attributes (modelica#3938)

I don't know exactly why, but these are causing some kind of problem in System Modeler, and I don't see why one would like to keep them.

Modelica/Electrical/QuasiStatic/UsersGuide/Overview/ACCircuit.mo

@@ -29,8 +29,7 @@ The voltage drop across the resistor
 <img
  border=\"0\"
  src=\"modelica://Modelica/Resources/Images/Electrical/QuasiStatic/UsersGuide/Overview/ACCircuit/img1.png\"
- alt=\"
-\\underline{v}_{r}=R\\underline{i}\">
+ alt=\"\\underline{v}_{r}=R\\underline{i}\">
 </div>
 
 <p>
@@ -41,8 +40,7 @@ and the inductor
 <img
  border=\"0\"
  src=\"modelica://Modelica/Resources/Images/Electrical/QuasiStatic/UsersGuide/Overview/ACCircuit/img2.png\"
- alt=\"
-\\underline{v}_{l}=j\\omega L\\underline{i}\">
+ alt=\"\\underline{v}_{l}=j\\omega L\\underline{i}\">
 </div>
 
 <p>
@@ -53,8 +51,7 @@ and the capacitor
 <img
  border=\"0\"
  src=\"modelica://Modelica/Resources/Images/Electrical/QuasiStatic/UsersGuide/Overview/ACCircuit/img3.png\"
- alt=\"
-\\underline{v}_{l}=j\\omega L\\underline{i}\">
+ alt=\"\\underline{v}_{l}=j\\omega L\\underline{i}\">
 </div>
 
 <p>
@@ -65,8 +62,7 @@ add up to the total voltage
 <img
  border=\"0\"
  src=\"modelica://Modelica/Resources/Images/Electrical/QuasiStatic/UsersGuide/Overview/ACCircuit/img4.png\"
- alt=\"
-\\underline{v}=\\underline{v}_{r}+\\underline{v}_{l}\">
+ alt=\"\\underline{v}=\\underline{v}_{r}+\\underline{v}_{l}\">
 </div>
 
 <p>